Align HT protection flags we send to iwm(4) firmware with flags used by

Align HT protection flags we send to iwm(4) firmware with flags used by
Linux iwlwifi.

Setting the FAT protection flag while we're using 20 MHz channels doesn't
really make a lot of sense to me but apparently firmware expects it to be
set regardless. Linux does not use the SELF_CTS_EN flag so it might be better
to avoid using SELF_CTS_EN.

According to zxystd from OpenIntelWireless, the same change fixed fatal
firmware errors seen during HT protection updates for them:
https://github.com/OpenIntelWireless/itlwm/commit/032a14185a434b7181c0e78a953dc2e1c21a0853

test and ok gnezdo@