wifi: mac80211: add an element parsing unit test

Add a unit test for the parsing of a fragmented sta profile
sub-element inside a fragmented multi-link element.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230827135854.333bc75df13f.I0ddfeb6a88a4d89e7c7850e8ef45a4b19b5a061a@changeid


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