• Add 11n HT40 support - i needed to send both HTINFO and HTCAP fields in the join message so the firmware would pick it up.

• Strip out the direct hardware fiddling for 40MHz mode - the firmware we're using doesn't require it (the rtl8712su firmware does; it is less 'fullmac' than what we're using.)

• Fix the mbuf handling during errors - rsu_tx shouldn't free mbufs; it's up to the caller to do so. This brings it in line with what other drivers do or should be doing.

Tested:

• RTL8712, HT40 channel, STA mode (during this commit)