mac80211: standardize adding supported rates IEs

Relocate the mesh implementation of adding the (extended) supported
rates IE to util.c, anticipating its use by other parts of mac80211.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Cc: Kalyan C Gaddam <chakkal@iit.edu>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
6 files changed