mac80211: Increase MAX_MSG_LEN

Looks that 100 chars isn't enough for messages, as we keep getting
warnings popping from different places due to message shortening.
Instead of trying to shorten the prints, just increase the buffer size.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>