module_param: check that bool parameters really are bool.

module_param(bool) used to counter-intuitively take an int.  In
fddd5201 (mid-2009) we allowed bool or int/unsigned int using a messy
trick.

This tightens the check (you'll get a warning about incompatible
return type) but still allows it.  Next kernel version, we'll remove
it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>