UPSTREAM: cfg80211: make BSSID generation function inline

This will enable reuse by mac80211.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
(cherry picked from commit 7ece9c372b21635120e7ab5ea3fc41ce9892ead8)
Bug: 154523213
Signed-off-by: Connor O'Brien <connoro@google.com>
Change-Id: I1db90bf0e255ae57955e2bdf663b1877c6c2df29