New helper in marshalling code: ncp_add_be32()

Takes host-endian argument, converts to big-endian and stores into packet
we are building.

A bunch of places in ncplib_kernel.c converted to using it.
Signed-off-by: Al Viro <viro@parcelfarce.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>