Add proto_tree_add_bitmask_with_flags.

It's proto_tree_add_bitmask with the ability to control the data appended to header.

Change-Id: Icce97437ba7cfc9158ec204a837da8db8138424a
Reviewed-on: https://code.wireshark.org/review/5533
Reviewed-by: Michael Mann <mmann78@netscape.net>