net80211: try to move m_defrag() / m_collapse() to the ieee80211_mbuf_adjust()

[avos]

Summary

Execute m_defrag() (or m_collapse(), depends on ic_seglimit variable) before submitting mbuf to the driver level. This should simplify error paths and remove two last stages from bus_dmamap_load_mbuf_sg() -(error)> m_collapse() -> bus_dmamap_load_mbuf_sg() sequence.

P.S. should it be added to the ieee80211_raw_output() too?

[adrian]

Nah, we can't go down this path right now.

The problem with this is figuring out what to do when (eg crypto, realign things, etc) shouldn't be in net80211. We may want to do this at a much later stage when we've tidied up the existing drivers quite a bit more; I don't want to keep churning things without finishing all the current changes we're making.

So I'm going to leave this open so we at least have it in here to look at, but I don't want to commit this to -HEAD.

Thanks though!