zebra: Allow fpm_listener to reject all routes

zebra: Allow fpm_listener to reject all routes

Now usage of `-r -f` with fpm_listener now causes all
routes to be rejected.

r1# sharp install routes 10.0.0.0 nexthop 192.168.44.5 5
r1# show ip route
Codes: K - kernel route, C - connected, L - local, 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, t - Table-Direct,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

IPv4 unicast VRF default:
D>o 10.0.0.0/32 [150/0] via 192.168.44.5, r1-eth0, weight 1, 00:00:02
D>o 10.0.0.1/32 [150/0] via 192.168.44.5, r1-eth0, weight 1, 00:00:02
D>o 10.0.0.2/32 [150/0] via 192.168.44.5, r1-eth0, weight 1, 00:00:02
D>o 10.0.0.3/32 [150/0] via 192.168.44.5, r1-eth0, weight 1, 00:00:02
D>o 10.0.0.4/32 [150/0] via 192.168.44.5, r1-eth0, weight 1, 00:00:02
C>* 192.168.44.0/24 is directly connected, r1-eth0, weight 1, 00:00:37
L>* 192.168.44.1/32 is directly connected, r1-eth0, weight 1, 00:00:37
r1#

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