ip: set fib_index before exiting input ACL node

ip: set fib_index before exiting input ACL node

While setting an ACL, a user can specify the adjacency to follow after
the input ACL node. Thus, we may skip a lookup and enter directly a
local node (ex: ip4_local). To prevent the local source check from
failing, we need to specify the fib index. And, we have to do it just
before exiting the input ACL node because the l2_classify object
is overlapping with the fib_index in the vnet_buffer_opaque_t struct.
We could have added a padding to avoid this overlap but there is no
place for that in the structure.

Type: fix

Signed-off-by: Arthur de Kerhor <arthurdekerhor@gmail.com>
Change-Id: I383c36e4aec08d181f966f28565aefed950d2a74