Enable DC filter in RT3071 Version E.
Initialize BBP68 to improve rx sensitivity.
Add RT2860_BCN_OFFSET1 and RT2860_MAX_LEN_CFG register initialization to
match with the vendor driver.  While here, remove unused RT2860_DEF_MAC
definition.
Don't treat the node as an 11n node if 11n rates are disabled.

For now, the AMRR code only knows about _either_ MCS or non-MCS rates.
It doesn't know how to downgrade (ie, doing 11b CCK rates if MCS0 isn't
reliable.)

PR:		kern/183428
Reset the timer interrupt status register at the top rather than bottom of
the interrupt handler.  If the event callback starts a new short timeout,
the timer can fire before returning from the event callback, and clearing
the interrupt status after that loses the interrupt and hangs until the
counter wraps.  Fixing all of this removes the need for the do-nothing
loop at the top of the handler which really just waited for the counter to
roll over and reach the one-shot count again.

Also add a missing return(0) in the periodic timer start case.
Enable USB.