mac80211: move skb info band assignment out

Instead of passing the band as a parameter to ieee80211_xmit()
and ieee80211_tx(), move it outside of the two functions while
making sure info->band is set up before calling them.

This removes the parameter and simplifies the follow commit.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc net/mac80211/cfg.c
Simple merge

diff --cc net/mac80211/ieee80211_i.h
Simple merge

diff --cc net/mac80211/sta_info.c
Simple merge

diff --cc net/mac80211/tx.c
Simple merge