mac80211: neaten ieee80211_deliver_skb

Remove the unnecessary duplicate test of "if (skb) {"
when !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.

Remove now unnecessary __maybe_unused, neaten comment
Remove unnecessary parenthesis around align cast.
Substitute reference to deprecated compare_ether_addr
with ether_addr_equal (in the comment.)

Signed-off-by: Joe Perches <joe@perches.com>
[edit commit log slightly]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>