netlink: backport of dynamic multicast groups support
kernel.org commits
2dbba6f773d1e1e4c78f03b0dbf19790d9017693 [GENETLINK]: Dynamic multicast groups
b4ff4f0419ae5db83553fab79d03a89c10d540a8 [NETLINK]: allocate group bitmaps dynamically
84659eb529b33572bb3f8c94e0978bd5d084bc7e [NETLIKN]: Allow removing multicast groups
2c04ddb707b4d50c314186249f466b6720ee4289 [GENETLINK]: Fix adjustment of number of multicast groups
79dc4386aec655ad829f320ab90888bacbc7037b [GENETLINK]: Fix race in genl_unregister_mc_groups()
3efb40c2c6eea315abcf19239c15d088e2498299 genetlink: export genl_unregister_mc_group()