iwlwifi: mvm: take the seqno from packet if transmit failed

commit ebea2f32e814445f94f9e087b646f1cf4d55fa5a upstream.

The fw is unreliable in all the cases in which the packet
wasn't sent.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>