netcat: remove CFLAGS modification from Makefile

It doesn't work well with some distros, so remove it entirely and just
use the path name in the #include lines instead.  That will work on all
systems.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
netcat: more Makefile cleanups

This fixes the Makefile to allow the module to be cross-compiled to
other architectures than the native one, as well as being able to be
built against a kernel that is not installed in /lib/modules.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>