MFC: Enlighten those who read the FINE POINTS of the documentation a
bit more on how ipfw(8) deals with tiny fragments. While we're at it,
add a quick log message to even let people know we dropped a
packet. (Note that the second FINE POINT is somewhat redundant given
the first, but since the code is there, leave the docs for it.)

src/sbin/ipfw/ipfw.8:		1.102
src/sys/netinet/ip_fw.c:	1.184