Swap segmentation Id when routing between subnets

Fixes bug 2052
https://gist.github.com/803a61717fdc153fde5a

Change-Id: I4f61531d5e58cf7969e8a26f80cc2c015338da54
Signed-off-by: Flavio Fernandes <ffernandes@redhat.com>
Signed-off-by: Dave Tucker <djt@redhat.com>