SOL_PACKET/PACKET_STATISTICS "getsockopt()" call, on Linux kernels that
support it, to get packet statistics, so that we can report the number
of dropped packets, and always use <linux/if_packet.h> to get
definitions for PF_PACKET sockets, so that we don't depend on glibc's
header files having been updated to support all the latest shiniest
kernel features (many systems with 2.4[.x] kernels don't have a
<netpacket/packet.h> that defines "struct tpacket_stats", for example,
so we wouldn't have been able to support that kernel feature on those
systems).
Guy Harris