MFC r283784:
Remove trailing whitespaces.

MFC r283785:
Require the embedded packet to contain 8 bytes after the IP header instead
of only 4. This is guaranteed by RFC 792 and the verification of GRE, ICMP
and TCP packets use 8 bytes.

MFC r283786:
There is no payload anymore. So compute the minimum packet length
correctly and use 40 as the default (if the minumum allows it), as
specified in the man page.

MFC r283806:
When the packet verification fails in verbose mode, print the correct
number of words in host byte order. Also remove a stray 'x'.

MFC r283808:
Don't send malformed SCTP probe packets.

MFC r283813:
Use an empty string for field descriptions of unknown protocols.

MFC r283817:
Don't send illegal packets when using UDP-Lite.

MFC r283819:
A TCP checksum of 0 is completely valid. Mapping 0 to 0xffff only
applies to UDP and UDP-Lite.

MFC r283820:
The code starts with base + 1 as the first port. Fix to documentation
to match that.