Remove *really* old PIM_OLD_KERNEL #ifdef

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Minor cleanup and refactor 'int datalen' --> 'size_t len'

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Fix issue #23: Handle ip_len correct (host byte order) on older BSD's

See issue #23 and https://wiki.freebsd.org/SOCK_RAW for details.  Thanks
to Olivier Cochard-Labbé for all the sparring help on this and his work
on FreeBSD!

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>
Remove *really* old Linux ip_csum anachronism (pre Linux 2.0)

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>