Remove a buggy comparision when setting manually the path MTU.
After fixing, the comparision would have become redundant.
Thanks to Andrew Galante for reporting the issue.

MFC after:	3 days
Add -K (__FreeBSD_version of kernel) and -U (__FreeBSD_version of userland).
Things like Makefile.inc1 resort to parsing /usr/include/osreldate.h with
awk because this isn't easily available by other means.  The separation
of user and kernel versions is important for jail/chroot environments.
Prevent an unlikely, but real double free issue in gvinum(8).

Coverity ID: 1018965