simplify STBC handling

Current STBC handler was waiting for peer caps to make decision.
Better way will be to make right decision on the host
and tell firmware what it can use.

This patch changes behaviour of firmware. Up now
host should send ATH_RC_TX_STBC_FLAG to enable STBC.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
ratectrl_11n_ln: nuke rcSibUpdate_11n

This function is reather useless. Side effect of it is a
filter for some bits which can be in other way implemented.
For now, i do not see any sense for this filter.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
nuke ath_hal_*xstbcsupport

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Update documentation to reflect the current reality.

Issue:	#28
Merge pull request #34 from olerem/rc

SImplefy STBC handler v4