Fix cfg80211_chandef_usable():
consider IEEE80211_VHT_CAP_EXT_NSS_BW when verifying 160/80+80 MHz.

Based on:
"Table 9-272 — Setting of the Supported Channel Width Set subfield and Extended NSS BW
Support subfield at a STA transmitting the VHT Capabilities Information field"
From "Draft P802.11REVmd_D3.0.pdf"
Signed-off-by: Aviad Brikman <aviad.brikman@celeno.com>
Signed-off-by: Shay Bar <shay.bar@celeno.com>
Link: https://lore.kernel.org/r/20200826143139.25976-1-shay.bar@celeno.com
[reformat the code a bit and use u32_get_bits()]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>