Revert "lantiq: xrx200: mark subtarget as source-only"

Revert "lantiq: xrx200: mark subtarget as source-only"

This reverts commit 0c117e1f6ccbee684ea0589d9024ca9dec4679c9.

Activate the lantiq/xrx200 target again.

There are still some problems with the GSWIP, but it is not leaking
packets to the wrong bridge in normal operations.
It shows some error messages at configuration like these:
[   54.308861] gswip 1e108000.switch: port 5 failed to add ce:9d:84:d1:81:f0 vid 1 to fdb: -22
[   54.325633] gswip 1e108000.switch: port 5 failed to add e8:de:27:95:c1:b4 vid 0 to fdb: -22
[   54.351242] gswip 1e108000.switch: port 5 failed to add e8:de:27:95:c1:b4 vid 1 to fdb: -22
[   54.358311] gswip 1e108000.switch: port 5 failed to delete ce:9d:84:d1:81:f0 vid 1 from fdb: -2

The problems are described in this pull request:
https://github.com/openwrt/openwrt/pull/13200

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit e1aaa1defd2340be3544dc614f905795b4d52f81)