ath9k: correct ath9k_hw_set_interrupts

ath9k: correct ath9k_hw_set_interrupts

Commit 4df3071ebd92ef7115b409da64d0eb405d24a631 "ath9k_hw: optimize
interrupt mask changes", changed ath9k_hw_set_interrupts function to
enable interrupts regardless of function argument, what could possibly
be wrong. Correct that behaviour and check "ints" arguments before
enabling interrupts, also disable interrupts if ints do not have
ATH9K_INT_GLOBAL flag set.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>