The Tunnel::yielding_teredo_decapsulation (on by default) makes it so
the Teredo analyzer doesn't attempt to decapsulate payloads when
there's already a sibling analyzer that thinks it's parsing the right
protocol. Sometimes, UDP payloads just happen to look like they are
validly Teredo-encapsulated and doing further analysis on the
decapsulated packet can quickly turn into a weird; this change helps
reduce such weirds.
