fib: only invoke adj delegate create callback on mcast adj create

fib: only invoke adj delegate create callback on mcast adj create

adj_delegate_adj_created() is incorrectly called when an existing
adj is found and returned. This can lead to crashes in some cases
in the pmtu delegate:

(gdb) bt
0  0x00007f2aa8fc9ce1 in raise () from /lib/x86_64-linux-gnu/libc.so.6
1  0x00007f2aa8fb3537 in abort () from /lib/x86_64-linux-gnu/libc.so.6
2  0x0000564361b5403a in os_exit (code=code@entry=1) at ./src/vpp/vnet/main.c:437
3  0x00007f2aa9271a3e in unix_signal_handler (signum=11, si=<optimized out>, uc=<optimized out>) at ./src/vlib/unix/main.c:188
4  <signal handler called>
5  0x00007f2aa9970d5a in fib_table_get_table_id_for_sw_if_index (proto=FIB_PROTOCOL_IP4, sw_if_index=<optimized out>) at ./src/vnet/fib/fib_table.c:1156
6  0x00007f2aa964aebf in ip_pmtu_adj_delegate_adj_created (ai=8) at ./src/vnet/ip/ip_path_mtu.c:197
7  0x00007f2aa9993ee5 in adj_delegate_adj_created (ai=ai@entry=8) at ./src/vnet/adj/adj_delegate.c:166
8  0x00007f2aa998dbde in adj_mcast_add_or_lock (proto=proto@entry=FIB_PROTOCOL_IP6, link_type=link_type@entry=VNET_LINK_IP6, sw_if_index=sw_if_index@entry=7) at ./src/vnet/adj/adj_mcast.c:95
9  0x00007f2aa95c7b3e in ip6_link_enable (sw_if_index=7, link_local_addr=link_local_addr@entry=0x0) at ./src/vnet/ip/ip6_link.c:217
10 0x00007f2aa9621587 in vl_api_sw_interface_ip_enable_disable_t_handler (mp=0x7f2a4fa5ad10) at ./src/vnet/ip/ip_api.c:108
11 0x00007f2aaa3b7e44 in msg_handler_internal (free_it=0, do_it=1, trace_it=<optimized out>, msg_len=<optimized out>, the_msg=0x7f2a4fa5ad10, am=0x7f2aaa3cc020 <api_global_main>) at ./src/vlibapi/api_shared.c:593
12 vl_msg_api_handler_no_free (the_msg=0x7f2a4fa5ad10, msg_len=<optimized out>) at ./src/vlibapi/api_shared.c:810
13 0x00007f2aaa3a1702 in vl_socket_process_api_msg (rp=<optimized out>, input_v=<optimized out>) at ./src/vlibmemory/socket_api.c:208
14 0x00007f2aaa3a95d8 in vl_api_clnt_process (vm=<optimized out>, node=<optimized out>, f=<optimized out>) at ./src/vlibmemory/memclnt_api.c:429
15 0x00007f2aa9226f37 in vlib_process_bootstrap (_a=<optimized out>) at ./src/vlib/main.c:1235
16 0x00007f2aa91824a8 in clib_calljmp () at /builds/graphiant/graphnos/vpp/debian/output/source_dir/src/vppinfra/longjmp.S:123
17 0x00007f2a47cf5d60 in ?? ()
18 0x00007f2aa922853f in vlib_process_startup (f=0x0, p=0x7f2a494dc000, vm=0x7f2a489ed680) at ./src/vlib/main.c:1260
19 dispatch_process (vm=0x7f2a489ed680, p=0x7f2a494dc000, last_time_stamp=<optimized out>, f=0x0) at ./src/vlib/main.c:1316
20 0x0000000000000000 in ?? ()
(gdb)

Type: fix

Change-Id: I2d3c041e0be8284471771c7882c89f743baab0e5
Signed-off-by: Peter Morrow <pdmorrow@gmail.com>