geneve: fix TOS inheriting for ipv4

The current code retrieves the TOS field after the lookup
on the ipv4 routing table. The routing process currently
only allows routing based on the original 3 TOS bits, and
not on the full 6 DSCP bits.
As a result the retrieved TOS is cut to the 3 bits.
However for inheriting purposes the full 6 bits should be used.

Extract the full 6 bits before the route lookup and use
that instead of the cut off 3 TOS bits.

Fixes: e305ac6c

 ("geneve: Add support to collect tunnel metadata.")
Signed-off-by: Matthias May <matthias.may@westermo.com>
Acked-by: Guillaume Nault <gnault@redhat.com>
Link: https://lore.kernel.org/r/20220805190006.8078-1-matthias.may@westermo.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>