mac80211: fix packet statistics for fast-RX

When adding per-CPU statistics, which added statistics back
to mac80211 for the fast-RX path, I evidently forgot to add
the "stats->packets++" line. The reason for that is likely
that I didn't see it since it's done in defragmentation for
the regular RX path.

Add the missing line to properly count received packets in
the fast-RX case.

Fixes: c9c5962b ("mac80211: enable collecting station statistics per-CPU")
Reported-by: Oren Givon <oren.givon@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>