stats: Make the crypt_packet stats balance

The tx_crypt stats only included data packets whereas the rx_crypt
stats included everything, because the TX was done in different places
and the RX in just the one.

I've added a 'stats_extra' structure so that the other threads can
update their own stats without extra locking, the get_stats call adds
them in as necessary.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>