Remove the oif=iface clause when tethering.

The rule is meant to be "iif=inputIface => lookup <table_for_outputIface>", not
"iif=foo oif=bar => lookup <table_for_bar>" (the latter would never match
because packets coming in on the input interface will not have any output
interface binding).

Bug: 16242255
Change-Id: I98a2a8ab90765aee833134297b58d4f7a212036f