bgpd : add prefix-length in show ip bgp neighbor advertised routes key

bgpd : add prefix-length in show ip bgp neighbor advertised routes key

Issue:
ip route 15.1.1.0/24 10.112.158.15
ip route 15.1.1.0/32 10.112.158.15
Brought up ebgp session between two FRR routers and
redistributed static routes via BGP and verfied the advertising
routes in the peer.

Verify the command "show ip  bgp neighbors <neighbor address>
advertised-routes json". It only shows 15.1.1.0/32 route details.

Root casue:
For both the routes "15.1.1.0/24" and "15.1.1.0/32" the advertised
routes key is the prefix i.e. "15.1.1.0".

Fix:
Modify the key to prefix/prefix-length.

Signed-off-by: Sarita Patra <saritap@vmware.com>