Add new lock for stageq (part of ieee80211_superg structure) and
ni_tx_superg (part of ieee80211_node structure);
drop com_lock protection where it is used to protect them.
While here, drop duplicate OPACKETS counter incrementation.
ni_tx_ampdu is not protected with it (however, it is also used without
locking in other places; probably, it requires some other solution
to be thread-safe).
Tested with RTL8188CUS (AP) and RTL8188EU (STA).
NOTE: Since this change breaks KBI, all wireless drivers need to be
recompiled.
Reviewed by: adrian
Approved by: re (gjb)
Differential Revision: https://reviews.freebsd.org/D6958
cdc0cf21eb