zebra: fix show ip route output

zebra: fix show ip route output

Variable "show ip route" commands invoke the same helper
(do_show_ip_route), potentially several times.

When asking to dump a non-default vrf, all vrfs or all tables, the
output is messy, the header summarizing abbreviations is repeated
several times, excess line feeds appear, the default table of default
VRF is concatenated to the previous table output...

Normalize the output:

- whatever the case, display the common header at most once, if there
  is at least an entry to dump.

- when using a "vrf all" or "table all" command, prepend a line with
  the VRF and table (even for the default vrf or table).

- when dumping a specific vrf or table, prepend a line with the VRF
  and table.

Example (vrf all)
=================

router# show ip route vrf all
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued route, r - rejected route

VRF main:
C>* 10.0.2.0/24 is directly connected, mgmt0, 00:24:09
K>* 10.0.2.2/32 [0/100] is directly connected, mgmt0, 00:24:09
C>* 10.125.0.0/24 is directly connected, ntfp2, 00:00:26

VRF private:
S>* 1.1.1.0/24 [1/0] via 10.125.0.2, loop0, 00:00:29
C>* 10.125.0.0/24 is directly connected, loop0, 00:00:42

Example (main vrf)
==================

router# show ip route
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued route, r - rejected route

C>* 10.0.2.0/24 is directly connected, mgmt0, 00:24:41
K>* 10.0.2.2/32 [0/100] is directly connected, mgmt0, 00:24:41
C>* 10.125.0.0/24 is directly connected, ntfp2, 00:00:58

Example (specific vrf)
======================

router# show ip route vrf private
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued route, r - rejected route

VRF private:
S>* 1.1.1.0/24 [1/0] via 10.125.0.2, loop0, 00:01:23
C>* 10.125.0.0/24 is directly connected, loop0, 00:01:36

Example (all tables)
====================

router# show ip route table all
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued route, r - rejected route

VRF main table 200:
S>* 4.4.4.4/32 [1/0] via 10.125.0.3, ntfp2, 00:01:51

VRF main table 254:
C>* 10.0.2.0/24 is directly connected, mgmt0, 00:25:34
K>* 10.0.2.2/32 [0/100] is directly connected, mgmt0, 00:25:34
C>* 10.125.0.0/24 is directly connected, ntfp2, 00:01:51

Example (all vrf, all table)
============================

router# show ip route table all vrf all
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued route, r - rejected route

VRF main table 200:
S>* 4.4.4.4/32 [1/0] via 10.125.0.3, ntfp2, 00:02:15

VRF main table 254:
C>* 10.0.2.0/24 is directly connected, mgmt0, 00:25:58
K>* 10.0.2.2/32 [0/100] is directly connected, mgmt0, 00:25:58
C>* 10.125.0.0/24 is directly connected, ntfp2, 00:02:15

VRF private table 200:
S>* 2.2.2.0/24 [1/0] via 10.125.0.2, loop0, 00:02:18

VRF private table 254:
S>* 1.1.1.0/24 [1/0] via 10.125.0.2, loop0, 00:02:18
C>* 10.125.0.0/24 is directly connected, loop0, 00:02:31

Example (specific table)
========================

router# show ip route table 200
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric,
       > - selected route, * - FIB route, q - queued route, r - rejected route

VRF main table 200:
S>* 4.4.4.4/32 [1/0] via 10.125.0.3, ntfp2, 00:05:26

Signed-off-by: Christophe Gouault <christophe.gouault@6wind.com>