*: Fix usage of bfd_adj_event

*: Fix usage of bfd_adj_event

Valgrind reports:

469901-==469901==
469901-==469901== Conditional jump or move depends on uninitialised value(s)
469901:==469901==    at 0x3A090D: bgp_bfd_dest_update (bgp_bfd.c:416)
469901-==469901==    by 0x497469E: zclient_read (zclient.c:3701)
469901-==469901==    by 0x4955AEC: thread_call (thread.c:1684)
469901-==469901==    by 0x48FF64E: frr_run (libfrr.c:1126)
469901-==469901==    by 0x213AB3: main (bgp_main.c:540)
469901-==469901==  Uninitialised value was created by a stack allocation
469901:==469901==    at 0x3A0725: bgp_bfd_dest_update (bgp_bfd.c:376)
469901-==469901==
469901-==469901== Conditional jump or move depends on uninitialised value(s)
469901:==469901==    at 0x3A093C: bgp_bfd_dest_update (bgp_bfd.c:421)
469901-==469901==    by 0x497469E: zclient_read (zclient.c:3701)
469901-==469901==    by 0x4955AEC: thread_call (thread.c:1684)
469901-==469901==    by 0x48FF64E: frr_run (libfrr.c:1126)
469901-==469901==    by 0x213AB3: main (bgp_main.c:540)
469901-==469901==  Uninitialised value was created by a stack allocation
469901:==469901==    at 0x3A0725: bgp_bfd_dest_update (bgp_bfd.c:376)

On looking at bgp_bfd_dest_update the function call into bfd_get_peer_info
when it fails to lookup the ifindex ifp pointer just returns leaving
the dest and src prefix pointers pointing to whatever was passed in.

Let's do two things:

a) The src pointer was sometimes assumed to be passed in and sometimes not.
Forget that.  Make it always be passed in
b) memset the src and dst pointers to be all zeros.  Then when we look
at either of the pointers we are not making decisions based upon random
data in the pointers.

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