wifi: mac80211: Add sta pointer sanity check in ieee80211_8023_xmit()

wifi: mac80211: Add sta pointer sanity check in ieee80211_8023_xmit()

Currently ieee80211_8023_xmit() accesses the sta pointer without any
sanity check, assuming that only unicast packets for an authorized
station are processed. But the sta pointer could become NULL when
a framework to support 802.3 offload for the multicast packets is
added in the follow-up patches. Add the valid sta pointer sanity
check to avoid the invalid pointer access.

This aligns with some of the subordinate functions called by
ieee80211_8023_xmit() that already NULL-check 'sta' such as
ieee80211_select_queue() and ieee80211_aggr_check().

Signed-off-by: Tamizh Chelvam Raja <tamizh.raja@oss.qualcomm.com>
Link: https://patch.msgid.link/20260604162403.1563729-2-tamizh.raja@oss.qualcomm.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>