pimd: Show all groups matched by an arbitrary prefix for `pim rp-info`

pimd: Show all groups matched by an arbitrary prefix for `pim rp-info`

```
r1# show ip pim rp-info
RP address       group/prefix-list   OIF               I am RP    Source   Group-Type
192.168.10.123   225.0.0.0/24        eth2              yes        Static   ASM
192.168.10.123   239.0.0.0/8         eth2              yes        Static   ASM
192.168.10.123   239.4.0.0/24        eth2              yes        Static   SSM

r1# show ip pim rp-info 239.4.0.0/25
RP address       group/prefix-list   OIF               I am RP    Source   Group-Type
192.168.10.123   239.0.0.0/8         eth2              yes        Static   ASM
192.168.10.123   239.4.0.0/24        eth2              yes        Static   SSM
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>