Usually, %dynamic is used as traffic selector for transport mode SAs,
however, if wildcard traps are used then the remote TS will be a subnet.
With strongSwan at the remote end that usually works fine as the local
%dynamic TS narrows the proposed TS appropriately. But some
implementations reject non-host TS for transport mode SAs.
Another problem could be if several distinct subnets are configured for a
wildcard trap, as we'd then propose unrelated subnets on that transport
mode SA, which might be problematic even for strongSwan (switch to tunnel
mode and duplicate policies).
Closesstrongswan/strongswan#61.