zebra: Allow one connected route per network mask on a interface

zebra: Allow one connected route per network mask on a interface

Currently FRR reads the kernel for interface state and FRR
creates a connected route per address on an interface.  If
you are in a situation where you have multiple addresses
on an interface just create 1 connected route for them:

sharpd@eva:/tmp/topotests$ vtysh -c "show int dummy302"
Interface dummy302 is up, line protocol is up
  Link ups:       0    last: (never)
  Link downs:     0    last: (never)
  vrf: default
  index 3279 metric 0 mtu 1500 speed 0
  flags: <UP,BROADCAST,RUNNING,NOARP>
  Type: Ethernet
  HWaddr: aa:4a:ed:95:9f:18
  inet 10.4.1.1/24
  inet 10.4.1.2/24 secondary
  inet 10.4.1.3/24 secondary
  inet 10.4.1.4/24 secondary
  inet 10.4.1.5/24 secondary
  inet6 fe80::a84a:edff:fe95:9f18/64
  Interface Type Other
  Interface Slave Type None
  protodown: off

sharpd@eva:/tmp/topotests$ vtysh -c "show ip route connected"
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, r - rejected, b - backup
       t - trapped, o - offload failure

C>* 10.4.1.0/24 is directly connected, dummy302, 00:10:03
C>* 192.168.161.0/24 is directly connected, enp39s0, 00:10:03

Signed-off-by: Donald Sharp <sharpd@nvidia.com>