VRRP: add a sample capture and two test cases

The sample capture consists of VRRPv2/IPv4, VRRPv3/IPv4 and VRRPv3/IPv6
packets. It was produced using 7 MikroTik devices running RouterOS 6.10
and configured for the same set of virtual addresses with different
priorities per device. The devices were powered on one after another
with a ~30 seconds delay in the order of VRRP priority ascending. The
test cases decode the capture with and without "-v".
Add support for VRRPv3 (IPv4 only).
VRRP: top off the previous change

Update the test cases and squelch a compiler warning.