This commit adds flags which will are applied if SNAT should be used on
the red address or any configured alias.
They prevent doing the SNAT when tranismitting packet through a VPN over the red interface.
Fixes #12162.
Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org> Tested-by: Michael Tremer <michael.tremer@ipfire.org> Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>