mac80211: tdls: disentangle HT supported conditions

mac80211: tdls: disentangle HT supported conditions

These conditions are rather difficult to follow, for example
because "!sta" only exists to not crash in the case that we
don't have a station pointer (WLAN_TDLS_SETUP_REQUEST) in
which the additional condition (peer supports HT) doesn't
actually matter anyway.

Cleaning this up only duplicates two lines of code but makes
the rest far easier to read, so do that.

As a side effect, smatch stops complaining about the lack of
a sta pointer test after the !sta (since the !sta goes away)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>