xfrm: no need to set DST_NOPOLICY in IPv4

xfrm: no need to set DST_NOPOLICY in IPv4

This is a cleanup patch following commit 7fed1a8a3596
("xfrm: fix "disable_policy" flag use when arriving from different devices")
which made DST_NOPOLICY no longer be used for inbound policy checks.

On outbound the flag was set, but never used.

As such, avoid setting it altogether and remove the nopolicy argument
from rt_dst_alloc().

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>