tproxy: Drop artificial port printing restriction

tproxy: Drop artificial port printing restriction

It does not make much sense to omit printing the port expression if it's
not a value expression: On one hand, input allows for more advanced
uses. On the other, if it is in-kernel, best nft can do is to try and
print it no matter what. Just ignoring ruleset elements can't be
correct.

Fixes: 2be1d52644cf7 ("src: Add tproxy support")
Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1721
Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>