wifi: mac80211: prevent VLANs on MLDs

Do not allow VLANs to be added to AP interfaces that are
MLDs, this isn't going to work because the link structs
aren't propagated to the VLAN interfaces yet.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20220902161144.8c88531146e9.If2ef9a3b138d4f16ed2fda91c852da156bdf5e4d@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>