mac80211: Print unknown packet type in tasklet_handler

In stress testing p54usb, the WARN_ON() in ieee80211_tasklet_handler() was
triggered; however, there is no logging of the received value for packet
type. Adding that feature will improve the warning.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>