selftests: fib_rule_tests: Add VRF match tests

selftests: fib_rule_tests: Add VRF match tests

Add tests for FIB rules that match on iif / oif being a VRF device. Test
both good and bad flows.

With previous patch ("net: fib_rules: Fix iif / oif matching on L3
master device"):

 # ./fib_rule_tests.sh
 [...]
 Tests passed: 328
 Tests failed:   0

Without it:

 # ./fib_rule_tests.sh
 [...]
 Tests passed: 324
 Tests failed:   4

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250414172022.242991-3-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>