ramips: restore full switch performance for USW-Flex

ramips: restore full switch performance for USW-Flex

Since commit f1c9afd80138 ("ramips: mt7621-dts: mux phy0/4 to gmac1") the
USW-Flex lan1 port has been attached directly to the CPU. This improves
routing performance but hinders switching.

This is a generally accepted trade-off in that commit but for USW-Flex it
is a questionable choice. This switch is designed to deliver PoE to remote
places and using it as a router is unlikely. Meanwhile, the lan1 port is
also PoE-in and will often be the uplink, carrying most of the traffic.

Reverting f1c9afd80138 for USW-Flex restores full 1 Gbps switching
performance on all ports.

Signed-off-by: Anders Melchiorsen <amelchio@nogoto.net>
Link: https://github.com/openwrt/openwrt/pull/17703
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit 62872f8bfd5c8bc80bb014417c6ed8057bbeb773)