selftests: net: vxlan: Add tests for vxlan nolocalbypass option.

Add test to make sure that the localbypass option is on by default.

Add test to change vxlan localbypass to nolocalbypass and check
that packets are delivered to userspace.

Signed-off-by: Vladimir Nikishkin <vladimir@nikishkin.pw>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>