mac80211: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple break statements instead of
letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/1a9c4e8248e76e1361edbe2471a68773d87f0b67.1605896060.git.gustavoars@kernel.org


Signed-off-by: Johannes Berg <johannes.berg@intel.com>