wifi: mac80211: mesh: check element parsing succeeded

ieee802_11_parse_elems() can return NULL, so we must
check for the return value.

Fixes: 5d24828d ("mac80211: always allocate struct ieee802_11_elems")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20231211085121.93dea364f3d3.Ie87781c6c48979fb25a744b90af4a33dc2d83a28@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>