Add the --disable-packet-ring configure option.

This allows the creation of 32-bit binaries that are compatible with
64-bit Linux kernels before version 2.6.27.

Original patch credit: David Fifield of the Nmap project
(https://svn.nmap.org/nmap/libpcap/NMAP_MODIFICATIONS/0002-Add-the-disable-packet-ring-configure-option.patch)