Make APF tests a bit more realistic.

1. Always make sure IPv4 and IPv6 packets have the right version
   nibble at the beginning. An upcoming change to the filter code
   will enforce this, at least for IPv6.
2. In verifyRaLifetime, when checking that an arbitrary change in
   the packet causes the RA to get dropped, don't use the first
   byte in the packet (which is the first byte in the source MAC
   address). This byte is not really meaningful to the RA and
   can be ignored by the filter. Instead, change something
   meaningful - a byte in the source address.

Bug: 66928272
Test: test-only change
Change-Id: If8d0e8b2701538d80eaaa57e9522c8828ccb27fb