Signed-off-by: Felix Fietkau <nbd@nbd.name>

Some drivers that do their own sequence number allocation (e.g. ath9k, mwlwifi) rely
on being able to modify params->ssn on starting tx ampdu sessions.
This was broken by a change that modified it to use sta->tid_seq[tid] instead.

Signed-off-by: Felix Fietkau <nbd@nbd.name>