wifi: mac80211: don't check carrier in chanctx code

We check here that we don't enable TX (netif_carrier_ok())
before we actually start using some channel context, but to
our knowledge this check has never triggered, and with MLO
it's just wrong since links can be added and removed much
more dynamically than before.

Simply remove the checks, there's no really good way to do
anything that would replace them.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>