ip tunnels: Fix erroneous calls to RT_TOS().

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2161351 Upstream Status: linux.git

Backport upstream merge commit 996237d9ba4d ("Merge branch 'do-not-use-rt_tos-for-ipv6-flowlabel'") to fix some invalid uses of the RT_TOS() macro (RT_TOS() clears high order DSCP bits which doesn't make sense for IPv6 and isn't appropriate when inheriting the DSCP value from the inner IP packet).

Upstream commit ab7e2e0dfa5d ("ipv6: do not use RT_TOS for IPv6 flowlabel") isn't part of this series since it has already been backported by Centos Stream commit 090d4736.

Also, there's a selftest upstream, which was introduced by commit b690842d12fd ("selftests/net: test l2 tunnel TOS/TTL inheriting"). This selftest isn't part of this series because it also tests inheritance from VLAN tagged frames, which Centos Stream doesn't currently support.

Signed-off-by: Guillaume Nault gnault@redhat.com