cfg80211: update information elements in cached BSS struct

When a cached BSS struct is updated because a new beacon was received,
the code replaces the cached information elements by the IEs from the
new beacon. However it did not update the pub.information_elements
and pub.len_information_elements fields leaving them either pointing
to the old beacon IEs or in an inconsistent state where the data is
replaced by the new beacon IEs but len_information_elements still has
its value from the first beacon.

Fix this by updating the information elements fields if they are
pointing to beacon IEs.

Signed-off-by: Sven Neumann <s.neumann@raumfeld.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>