isisd: Fix usage of uninited memory

isisd: Fix usage of uninited memory

valgrind is showing a usage of uninited memory:

==935465== Conditional jump or move depends on uninitialised value(s)
==935465==    at 0x159E17: tlvs_area_addresses_to_adj (isis_tlvs.c:4430)
==935465==    by 0x15A4BD: isis_tlvs_to_adj (isis_tlvs.c:4568)
==935465==    by 0x1377F0: process_p2p_hello (isis_pdu.c:203)
==935465==    by 0x1391FD: process_hello (isis_pdu.c:781)
==935465==    by 0x13BDBE: isis_handle_pdu (isis_pdu.c:1700)
==935465==    by 0x13BECD: isis_receive (isis_pdu.c:1744)
==935465==    by 0x49210FF: thread_call (thread.c:1585)
==935465==    by 0x48CFACB: frr_run (libfrr.c:1099)
==935465==    by 0x1218C9: main (isis_main.c:272)
==935465==
==935465== Conditional jump or move depends on uninitialised value(s)
==935465==    at 0x483EEC5: bcmp (vg_replace_strmem.c:1111)
==935465==    by 0x15A290: tlvs_ipv4_addresses_to_adj (isis_tlvs.c:4512)
==935465==    by 0x15A4EB: isis_tlvs_to_adj (isis_tlvs.c:4570)
==935465==    by 0x1377F0: process_p2p_hello (isis_pdu.c:203)
==935465==    by 0x1391FD: process_hello (isis_pdu.c:781)
==935465==    by 0x13BDBE: isis_handle_pdu (isis_pdu.c:1700)
==935465==    by 0x13BECD: isis_receive (isis_pdu.c:1744)
==935465==    by 0x49210FF: thread_call (thread.c:1585)
==935465==    by 0x48CFACB: frr_run (libfrr.c:1099)
==935465==    by 0x1218C9: main (isis_main.c:272)

Effectively we are reallocing memory to hold data.  realloc does not
set the new memory to anything.  So whatever happens to be in the memory
is what is there.  after the realloc happens we are iterating over the
memory just realloced and doing memcmp's to values in it causing these
use of uninitialized memory.

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