Merge branch 'xfrm: Convert __xfrm4_dst_lookup() and its callers to dscp_t.'

Guillaume Nault says:

====================
This patch series continues to prepare users of ->flowi4_tos to a
future conversion of this field (__u8 to dscp_t). This time, we convert
__xfrm4_dst_lookup() and its call chain.

The objective is to eventually make all users of ->flowi4_tos use a
dscp_t value. Making ->flowi4_tos a dscp_t field will help avoiding
regressions where ECN bits are erroneously interpreted as DSCP bits.
====================

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>