cfg80211: Fix country IE parsing for single channel triplets

This enhances the way we parse country IEs to minimize
the number of regulatory rules that we create. It also fixes
our current implementation which treated country IE triplets
with only one channel as one independed regulatory rule even
though adjecent rules were also being provided.

Without this patch APs which send country IE information with
a channel triplet for each individual channel will force cfg80211
to deny HT40 operation as a regulatory rule would have been created
independently for each channel and as such configured only for
20 MHz operation.

Although 802.11n APs which send country IEs triplets in this fassion
are likely rare Benoit reports this against the Ubiquity NanoStation M5,
with Country "FR" and HT40 enabled.

Since we now have a helper which parses the triplets in intermediate
steps we now take care extra care to process padding.

Reported-by: Benoit PAPILLAULT <benoit.papillault@free.fr>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>