tests/netinet: add few tests for sending a broadcast packet

[glebius]

Summary

1. Set SO_BROADCAST and send to INADDR_BROADCAST. This one is broken since at least FreeBSD 6.0, see bug 99558. Today it sends packet to a non-broadcast link level address.
2. Set SO_BROADCAST, set IP_ONESBCAST and send to local broadcast address.
3. Set SO_BROADCAST and send to local broadcast address.

For each test we bind a second socket to check whether the broadcast
is actually received.

PR: 99558

[glebius]

Make IP_ONESBCAST test more sophisticated: on machines with more interfaces
do more testing.