net80211: add support for sequence number offloading

[adrian]

Summary

Add support for sequence number offloading -

• Check IEEE80211_CONF_SEQNO_OFFLOAD() before doing TX lock manipulation;
• Don't call ieee80211_output_seqno_assign() if IEEE80211_CONF_SEQNO_OFFLOAD() is true.

TODO:

• this doesn't yet do beacon sequence number allocation offloading; I'll tackle that later.

[adrian]

Note: my hope is to eventually delete the TX lock entirely; this sets the ground work to first experiment and test various drivers in this stack.

[bz]

Ignoring the open question on the TODO this seems fine.

sys/net80211/ieee80211_output.c

3863

When is this supposed to be done? Before or after this lands?

[adrian]

sys/net80211/ieee80211_output.c

3863

after, because I am not yet sure if I have to split the two into different flags or not.
Doing this work doesn't hurt anything, the beacon numbers will keep incrementing.