The code validates the HE capability element size later,
but slightly wrong, so use the new helper to do it right
and only accept it if it has a good size.

Link: https://lore.kernel.org/r/20220214172920.b5b06f264a61.I645ac1e2dc0ace223ef3e551cd5a71c88bd55e04@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>