xfrm: Only add l3mdev oif to dst lookups

Subash reported that commit 42a7b32b ("xfrm: Add oif to dst lookups")
broke a wifi use case that uses fib rules and xfrms. The intent of
42a7b32b was driven by VRFs with IPsec. As a compromise relax the
use of oif in xfrm lookups to L3 master devices only (ie., oif is either
an L3 master device or is enslaved to a master device).

Fixes: 42a7b32b

 ("xfrm: Add oif to dst lookups")
Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>