virNetlinkDumpCommand: Don't leak response buffer

virNetlinkDumpCommand: Don't leak response buffer

==16451== 32,768 bytes in 2 blocks are definitely lost in loss record 1,007 of 1,013
==16451==    at 0x4C2AF0F: malloc (vg_replace_malloc.c:299)
==16451==    by 0x7CADB40: nl_recv (in /usr/lib64/libnl-3.so.200.23.0)
==16451==    by 0x532DFAC: virNetlinkDumpCommand (virnetlink.c:363)
==16451==    by 0x53236AE: virNetDevIPCheckIPv6Forwarding (virnetdevip.c:641)
==16451==    by 0xE3E4A1A: networkStartNetworkVirtual (bridge_driver.c:2490)
==16451==    by 0xE3E55F5: networkStartNetwork (bridge_driver.c:2832)
==16451==    by 0xE3DFFE5: networkAutostartConfig (bridge_driver.c:531)
==16451==    by 0x53F47E0: virNetworkObjListForEachHelper (virnetworkobj.c:1412)
==16451==    by 0x52FE69F: virHashForEach (virhash.c:606)
==16451==    by 0x53F4857: virNetworkObjListForEach (virnetworkobj.c:1439)
==16451==    by 0xE3E0BF4: networkStateAutoStart (bridge_driver.c:808)
==16451==    by 0x55689CE: virStateInitialize (libvirt.c:758)

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>