LinuxKPi: lkpi___kmalloc change a < into <= for proper boundry check

lkpi___kmalloc() would use contigmalloc if the requested size is exactly
PAGE_SIZE. But we can still fullfill this request from malloc() without
losing the guarantee of physical contiguous memory.

Sponsored by: The FreeBSD Foundation
Reported by: emaste (in D46656)
Fixes: 19df0c5abcb9d
Reviewed by: dumbbell, emaste
Differential Revision: https://reviews.freebsd.org/D49570

(cherry picked from commit 19efc9e6320a30e230b0b40d5bae90142ec13aeb)