Mega-commit fixing several outstanding issues with the port.
Fix inconsistent configure-time behaviour. Previously, the tcpdump port
would look at the base system pcap, then attempt to link against the port.
This caused spurious link failures, and should fix build on IA64.
Add a new switch, WITH_LIBPCAP_PORT, to force the use of libpcap
Rototile the build-time options for the port, and document them.
Fix detection of the OpenSSL libraries; 0.9.7d and later renamed the
des_cbc_encrypt function to DES_cbc_encrypt, so deal with this by
rebuilding configure after patching configure.in.
Incorporate fix for PR bin/76497 suggested by keramida@ (logic error
in the PPP IPV6CP parser).
Make some stylistic fixes while we're at it, and improve comments.
Mark as unbroken on -CURRENT.
PR: bin/76497 (possibly others)