Fix libpcap issue #893: check for invalid IPv4 addresses.

This fixes errors such as:

tcpdump -i lagg0 net 999.999.999.999

This was originally discovered on a Red Hat 7.7 server and verified
to also be a bug on FreeBSD.

Obtained from: https://github.com/the-tcpdump-group/libpcap/commit/ \

		07070918d5e81a515315b395f334e52589fe0fb

Fixed by: https://github.com/guyharris