zebra: zebra crash for zapi stream

zebra: zebra crash for zapi stream

Issue:
If static route is created with a BGP route as nexthop, which
recursively resolves over 512 ECMP v6 nexthops, zapi nexthop encode
fails, as there is not enough memory allocated for stream. This causes
assert/core dump in zebra. Right now we allocate fixed memory
of ZEBRA_MAX_PACKET_SIZ size.

Fix:
1)Dynamically calculate required memory size for the stream
2)try to optimize memory usage

Testing:
No crash happens anymore with the fix
zebra: zebra crash for zapi stream

Issue:
If static route is created with a BGP route as nexthop, which
recursively resolves over 512 ECMP v6 nexthops, zapi nexthop encode
fails, as there is not enough memory allocated for stream. This causes
assert/core dump in zebra. Right now we allocate fixed memory
of ZEBRA_MAX_PACKET_SIZ size.

Fix:
1)Dynamically calculate required memory size for the stream
2)try to optimize memory usage

Testing:
No crash happens anymore with the fix
r1#
r1# sharp install routes 2100:cafe:: nexthop 2001:db8::1 1000
r1#

r2# conf
r2(config)# ipv6 route 2503:feca::100/128 2100:cafe::1
r2(config)# exit
r2#

Signed-off-by: Soumya Roy <souroy@nvidia.com>