zebra: Fix use after deletion event in freebsd

zebra: Fix use after deletion event in freebsd

In the FreeBSD code if you delete the interface
and it has no configuration, the ifp pointer will
be deleted from the system *but* zebra continues
to dereference the just freed pointer.

==58624== Invalid read of size 1
==58624==    at 0x48539F3: strlcpy (in /usr/local/libexec/valgrind/vgpreload_memcheck-amd64-freebsd.so)
==58624==    by 0x2B0565: ifreq_set_name (ioctl.c:48)
==58624==    by 0x2B0565: if_get_flags (ioctl.c:416)
==58624==    by 0x2B2D9E: ifan_read (kernel_socket.c:455)
==58624==    by 0x2B2D9E: kernel_read (kernel_socket.c:1403)
==58624==    by 0x499F46E: thread_call (thread.c:2002)
==58624==    by 0x495D2B7: frr_run (libfrr.c:1196)
==58624==    by 0x2B40B8: main (main.c:471)
==58624==  Address 0x6baa7f0 is 64 bytes inside a block of size 432 free'd
==58624==    at 0x484ECDC: free (in /usr/local/libexec/valgrind/vgpreload_memcheck-amd64-freebsd.so)
==58624==    by 0x4953A64: if_delete (if.c:283)
==58624==    by 0x2A93C1: if_delete_update (interface.c:874)
==58624==    by 0x2B2DF3: ifan_read (kernel_socket.c:453)
==58624==    by 0x2B2DF3: kernel_read (kernel_socket.c:1403)
==58624==    by 0x499F46E: thread_call (thread.c:2002)
==58624==    by 0x495D2B7: frr_run (libfrr.c:1196)
==58624==    by 0x2B40B8: main (main.c:471)
==58624==  Block was alloc'd at
==58624==    at 0x4851381: calloc (in /usr/local/libexec/valgrind/vgpreload_memcheck-amd64-freebsd.so)
==58624==    by 0x496A022: qcalloc (memory.c:116)
==58624==    by 0x49546BC: if_new (if.c:164)
==58624==    by 0x49546BC: if_create_name (if.c:218)
==58624==    by 0x49546BC: if_get_by_name (if.c:603)
==58624==    by 0x2B1295: ifm_read (kernel_socket.c:628)
==58624==    by 0x2A7FB6: interface_list (if_sysctl.c:129)
==58624==    by 0x2E99C8: zebra_ns_enable (zebra_ns.c:127)
==58624==    by 0x2E99C8: zebra_ns_init (zebra_ns.c:214)
==58624==    by 0x2B3FF2: main (main.c:401)
==58624==

Zebra needs to pass back whether or not the ifp pointer
was freed when if_delete_update is called and it should
then check in ifan_read as well as ifm_read that the
ifp pointer is still valid for use.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>