module: Modify module_flags() to accept show_state argument

No functional change.

With this patch a given module's state information (i.e. 'mod->state')
can be omitted from the specified buffer. Please note that this is in
preparation to include the last unloaded module's taint flag(s),
if available.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>