zebra: Cleanup the memory from the hash for MPLS stuff

zebra: Cleanup the memory from the hash for MPLS stuff

==1595641== 280 (80 direct, 200 indirect) bytes in 1 blocks are definitely lost in loss record 30 of 38
==1595641== at 0x483AB65: calloc (vg_replace_malloc.c:760)
==1595641== by 0x493C89C: qcalloc (memory.c:116)
==1595641== by 0x1E8426: lsp_alloc (zebra_mpls.c:1116)
==1595641== by 0x49147F1: hash_get (hash.c:162)
==1595641== by 0x1EC880: mpls_lsp_install (zebra_mpls.c:3192)
==1595641== by 0x1C51BB: zread_vrf_label (zapi_msg.c:3197)
==1595641== by 0x1C6F11: zserv_handle_commands (zapi_msg.c:3863)
==1595641== by 0x24D0F4: zserv_process_messages (zserv.c:523)
==1595641== by 0x498F4CC: thread_call (thread.c:2002)
==1595641== by 0x49253A2: frr_run (libfrr.c:1198)
==1595641== by 0x1A28BA: main (main.c:475)
==1595641==
==1595641== 1,400 (400 direct, 1,000 indirect) bytes in 5 blocks are definitely lost in loss record 35 of 38
==1595641== at 0x483AB65: calloc (vg_replace_malloc.c:760)
==1595641== by 0x493C89C: qcalloc (memory.c:116)
==1595641== by 0x1E8426: lsp_alloc (zebra_mpls.c:1116)
==1595641== by 0x49147F1: hash_get (hash.c:162)
==1595641== by 0x1EBD7C: mpls_zapi_labels_process (zebra_mpls.c:2915)
==1595641== by 0x1C35D9: zread_mpls_labels_add (zapi_msg.c:2513)
==1595641== by 0x1C6F11: zserv_handle_commands (zapi_msg.c:3863)
==1595641== by 0x24D0F4: zserv_process_messages (zserv.c:523)
==1595641== by 0x498F4CC: thread_call (thread.c:2002)
==1595641== by 0x49253A2: frr_run (libfrr.c:1198)
==1595641== by 0x1A28BA: main (main.c:475)

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>