ath9k: add an extra boolean parameter to ath9k_hw_apply_txpower

In order to unifying regulatory limit handling
commit ca2c68cc
(ath9k_hw: clean up tx power handling) introduced
a new helper function 'ath9k_hw_apply_txpower',
and the direct calls of 'ah->eep_ops->set_txpower'
has been replaced by a call of the helper function.

This caused a change in the behaviour of the
'ath9k_hw_set_txpowerlimit' function. The purpose
of that function is to calculate and store the
rate txpower table and the regulatory limit without
touching the hardware registers. Before the commit,
the 'test' parameter of the function was passed to
the 'ah->eep_ops->set_txpower'. Now the calling of
the 'set_txpower' function happens indirectly through
'ath9k_hw_apply_txpower', so the 'test' argument of
the 'set_txpower' is always 'false'.

This patch restores the original behaviour of
'ath9k_hw_set_txpowerlimit' by adding a new
argument to 'ath9k_hw_apply_txpower.'

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>