mwifiex: send regulatory domain info to firmware only if alpha2 changed

On cfg80211 regulatory domain change, drivers gets alpha2 country
code or "00" in driver's notification handler.

In most cases, the pattern will be US, 00, US, 00, US, 00, US, ...
There is no need to send domain info to firmware in case of "00" or
with the same alpha2 country code.

Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>