pim6d: Fix memory leaks

pim6d: Fix memory leaks

Problem Statement:
========================
Mentioning few of the leaks here:

=3843268== 6 bytes in 3 blocks are still reachable in loss record 1 of 29
==3843268==    at 0x483C855: malloc (vg_replace_malloc.c:381)
==3843268==    by 0x489ED0E: qmalloc (memory.c:106)
==3843268==    by 0x48DE8DB: redist_add_instance (zclient.c:125)
==3843268==    by 0x48DF561: zclient_init (zclient.c:647)
==3843268==    by 0x14FFA3: pim_zebra_init (pim_zebra.c:527)
==3843268==    by 0x11D021: main (pim6_main.c:178)
==3843268==
==3843268== 24 bytes in 1 blocks are still reachable in loss record 2 of 29
==3843268==    at 0x484147B: calloc (vg_replace_malloc.c:1328)
==3843268==    by 0x489EE03: qcalloc (memory.c:111)
==3843268==    by 0x4878DDE: buffer_new (buffer.c:72)
==3843268==    by 0x48DE7BF: zclient_new (zclient.c:75)
==3843268==    by 0x14FF1D: pim_zebra_init (pim_zebra.c:516)
==3843268==    by 0x11D021: main (pim6_main.c:178)
==3843268==
==3843268== 24 bytes in 1 blocks are still reachable in loss record 3 of 29
==3843268==    at 0x484147B: calloc (vg_replace_malloc.c:1328)
==3843268==    by 0x489EE03: qcalloc (memory.c:111)
==3843268==    by 0x4878DDE: buffer_new (buffer.c:72)
==3843268==    by 0x48DE7BF: zclient_new (zclient.c:75)
==3843268==    by 0x150A3D: zclient_lookup_new (pim_zlookup.c:131)
==3843268==    by 0x11D021: main (pim6_main.c:178)

RCA:
=======================
Memory is allocated when the daemon started but
it is not freed when terminated.

Fix:
=======================
Freeing the memory when daemon goes down.

Signed-off-by: Mobashshera Rasool <mrasool@vmware.com>