wlcore: save seq num only between recoveries

We want seq num (freed_pkts) to be initialized
on each new connection, but keep persistent
between recoveries/suspends.

Save the freed_pkts in the private block of the
sta struct (we already do a similar thing for
AP's stations).

However, keep the old wlvif->total_freed_pkts
in order to avoid too intrusive change.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>