zebra: ra lifetime and interval check

[soumyar-roy]

when ra lifetime is 0, the interval check of lessthan lifetime should not be done.

Ticket: #4205240 Testing: root@r1:mgmt:/var/log/frr# nv set interface swp3 ip neighbor-discovery router-advertisement interval 10000 created [rev_id: 15] root@r1:mgmt:/var/log/frr# nv set interface swp3 ip neighbor-discovery router-advertisement lifetime 0 root@r1:mgmt:/var/log/frr# nv config apply applied [rev_id: 15]

interface swp3 ipv6 nd prefix 2001:cccc:1::/64 ipv6 nd prefix 2001:db8:1::/64 2592000 600 ipv6 nd prefix 2001:dddd:1::/64 ipv6 nd prefix 2008::/64 no-autoconfig ipv6 nd ra-interval 10 ipv6 nd ra-lifetime 0 no ipv6 nd suppress-ra exit

Tcpdump 17:59:57.573946 IP6 (flowlabel 0x849e8, hlim 255, next-header ICMPv6 (58) payload length: 152) fe80::202:ff:fe00:b > ip6-allnodes: [icmp6 sum ok] ICMP6, router advertisement, length 152 hop limit 64, Flags [none], pref medium, router lifetime 0s, reachable time 0ms, retrans timer 0ms prefix info option (3), length 32 (4): 2001:db8:1::/64, Flags [onlink, auto], valid time 2592000s, pref. time 600s 0x0000: 40c0 0027 8d00 0000 0258 0000 0000 2001 0x0010: 0db8 0001 0000 0000 0000 0000 0000 prefix info option (3), length 32 (4): 2001:cccc:1::/64, Flags [onlink, auto], valid time 2592000s, pref. time 604800s 0x0000: 40c0 0027 8d00 0009 3a80 0000 0000 2001 0x0010: cccc 0001 0000 0000 0000 0000 0000 prefix info option (3), length 32 (4): 2001:dddd:1::/64, Flags [onlink, auto], valid time 2592000s, pref. time 604800s 0x0000: 40c0 0027 8d00 0009 3a80 0000 0000 2001 0x0010: dddd 0001 0000 0000 0000 0000 0000 prefix info option (3), length 32 (4): 2008::/64, Flags [onlink], valid time 2592000s, pref. time 604800s 0x0000: 4080 0027 8d00 0009 3a80 0000 0000 2008 0x0010: 0000 0000 0000 0000 0000 0000 0000 source link-address option (1), length 8 (1): 00:02:00:00:00:0b 0x0000: 0002 0000 000b