bgpd: Fix debug output for route-map names when using a unsuppress-map

bgpd: Fix debug output for route-map names when using a unsuppress-map

Log is printing this with this config:

2023-03-28 07:36:47.007 [DEBG] bgpd: [Q9J6Z-09HRR] 192.168.119.120 [Update:SEND] 1.2.3.33/32 is filtered by route-map '(null)'

Here's the config:

 address-family ipv4 unicast
  network 1.2.3.33/32
  network 1.2.3.34/32
  aggregate-address 1.2.3.0/24 summary-only
  redistribute table 33 route-map foo
  neighbor 192.168.119.120 route-map DENY in
  neighbor 192.168.119.120 unsuppress-map UNSUPPRESS

ip prefix-list UNSUPPRESS seq 5 permit 1.2.3.4/32
ip prefix-list UNSUPPRESS seq 10 permit 1.2.3.5/32
ip prefix-list UNSUPPRESS seq 15 permit 1.2.3.6/32

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