selftests: Add tests for vrf and xfrms

Add tests for vrf and xfrms with a second round after adding a
qdisc. There are a few known problems documented with the test
cases that fail. The fix is non-trivial; will come back to it
when time allows.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>