ip_options_compile: properly handle unaligned pointer

The current code takes an unaligned pointer and does htonl() on it to
make it big-endian, then does a memcpy().  The problem is that the
compiler decides that since the pointer is to a __be32, it is legal
to optimize the copy into a processor word store.  However, on an
architecture that does not handled unaligned writes in kernel space,
this produces an unaligned exception fault.

The solution is to track the pointer as a "char *" (which removes a bunch
of unpleasant casts in any case), and then just use put_unaligned_be32()
to write the value to memory.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: David S. Miller <davem@zippy.davemloft.net>