netfilter: nft_fib: Fix for rpath check with VRF devices

netfilter: nft_fib: Fix for rpath check with VRF devices

[ Upstream commit 447714c7b36ff1079380e5f5f2f71346fb58ebb4 ]

Analogous to commit c5dfc36d390e7 ("netfilter: Fix rpfilter
dropping vrf packets by mistake") but for nftables fib expression:
Add special treatment of VRF devices so that typical reverse path
filtering via 'fib saddr . iif oif' expression works as expected.

Fixes: 5b1de3fa6d053 ("netfilter: nf_tables: add fib expression")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>