lib, zebra: Do not have duplicate memory type problems

lib, zebra: Do not have duplicate memory type problems

In zebra_mpls.c it has a usage of MTYPE_NH_LABEL which is
defined in both lib/nexthop.c and zebra/zebra_mpls.c.  The
usage in zebra_mpls.c is a realloc.  This leads to a crash:

(gdb) bt
0  __pthread_kill_implementation (no_tid=0, signo=6, threadid=126487246404032) at ./nptl/pthread_kill.c:44
1  __pthread_kill_internal (signo=6, threadid=126487246404032) at ./nptl/pthread_kill.c:78
2  __GI___pthread_kill (threadid=126487246404032, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
3  0x0000730a1b442476 in __GI_raise (sig=6) at ../sysdeps/posix/raise.c:26
4  0x0000730a1b94fb18 in core_handler (signo=6, siginfo=0x7ffeed1e07b0, context=0x7ffeed1e0680) at lib/sigevent.c:268
5  <signal handler called>
6  __pthread_kill_implementation (no_tid=0, signo=6, threadid=126487246404032) at ./nptl/pthread_kill.c:44
7  __pthread_kill_internal (signo=6, threadid=126487246404032) at ./nptl/pthread_kill.c:78
8  __GI___pthread_kill (threadid=126487246404032, signo=signo@entry=6) at ./nptl/pthread_kill.c:89
9  0x0000730a1b442476 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
10 0x0000730a1b4287f3 in __GI_abort () at ./stdlib/abort.c:79
11 0x0000730a1b9984f5 in _zlog_assert_failed (xref=0x730a1ba59480 <_xref.16>, extra=0x0) at lib/zlog.c:789
12 0x0000730a1b8f8908 in mt_count_free (mt=0x576e0edda520 <MTYPE_NH_LABEL>, ptr=0x576e36617b80) at lib/memory.c:74
13 0x0000730a1b8f8a59 in qrealloc (mt=0x576e0edda520 <MTYPE_NH_LABEL>, ptr=0x576e36617b80, size=16) at lib/memory.c:112
14 0x0000576e0ec85e2e in nhlfe_out_label_update (nhlfe=0x576e368895f0, nh_label=0x576e3660e9b0) at zebra/zebra_mpls.c:1462
15 0x0000576e0ec833ff in lsp_install (zvrf=0x576e3655fb50, label=17, rn=0x576e366197c0, re=0x576e3660a590) at zebra/zebra_mpls.c:224
16 0x0000576e0ec87c34 in zebra_mpls_lsp_install (zvrf=0x576e3655fb50, rn=0x576e366197c0, re=0x576e3660a590) at zebra/zebra_mpls.c:2215
17 0x0000576e0ecbb427 in rib_process_update_fib (zvrf=0x576e3655fb50, rn=0x576e366197c0, old=0x576e36619660, new=0x576e3660a590) at zebra/zebra_rib.c:1084
18 0x0000576e0ecbc230 in rib_process (rn=0x576e366197c0) at zebra/zebra_rib.c:1480
19 0x0000576e0ecbee04 in process_subq_route (lnode=0x576e368e0270, qindex=8 '\b') at zebra/zebra_rib.c:2661
20 0x0000576e0ecc0711 in process_subq (subq=0x576e3653fc80, qindex=META_QUEUE_BGP) at zebra/zebra_rib.c:3226
21 0x0000576e0ecc07f9 in meta_queue_process (dummy=0x576e3653fae0, data=0x576e3653fb80) at zebra/zebra_rib.c:3265
22 0x0000730a1b97d2a9 in work_queue_run (thread=0x7ffeed1e3f30) at lib/workqueue.c:282
23 0x0000730a1b96b039 in event_call (thread=0x7ffeed1e3f30) at lib/event.c:1996
24 0x0000730a1b8e4d2d in frr_run (master=0x576e36277e10) at lib/libfrr.c:1232
25 0x0000576e0ec35ca9 in main (argc=7, argv=0x7ffeed1e4208) at zebra/main.c:536

Clearly replacing a label stack is an operation that should be owned by
lib/nexthop.c.  So lets move this function into there and have
zebra_mpls.c just call the function to replace the label stack.

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