qcacld-3.0: Add lock for multicast list update

Currently, kernel provides the multicast address list to the driver
and driver appends this list with new peer multicast address which
are not included in the list. This is done in irq thread.
But with recent changes, for NDI, driver will update this list on
the peer addition and deletion which is executed in scheduler thread.
This may lead to issue when request to update the multicast
list comes from scheduler thread while irq thread request is in
progress and vice-versa.
So, to handle such situation, add spin lock which will protect the
multicast address list.

Change-Id: I9093a92d3714abd875dcd02743f711a5bed26090
CRs-Fixed: 3518989