eth1394: replace __constant_htons by htons

...and __constant_ntohs, __constant_ntohl, __constant_cpu_to_be32 too
where possible.  Htons and friends are resolved to constants in these
places anyway.  Also fix an endianess glitch in a log message, spotted
by Alexey Dobriyan.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Ben Collins <bcollins@ubuntu.com>