Remove the search back up the proto tree for the capture frequency that was

Remove the search back up the proto tree for the capture frequency that was
being used to determine if we are dissecting 802.11ad in several places.

Since we now have a macro for testing that and the frequency is in the phdr
we really should use that. This also prevents problems during display filter
execution with respect to fields that are only present for 802.11ad.

Change-Id: Id04a31c15b04378b6b0f056baa1f37d94a65b71c
Signed-off-by: Richard Sharpe <realrichardsharpe@gmail.com>
Reviewed-on: https://code.wireshark.org/review/10234
Reviewed-by: Guy Harris <guy@alum.mit.edu>