genetlink: export genl_unregister_mc_group()

Add an EXPORT_SYMBOL() to genl_unregister_mc_group(), to allow
unregistering groups on the run. EXPORT_SYMBOL_GPL() is not used as
the rest of the functions exported by this module (eg:
genl_register_mc_group) are also not _GPL().

Cleanup is currently done when unregistering a family, but there is
no way to unregister a single multicast group due to that function not
being exported. Seems to be a mistake as it is documented as for
external consumption.

This is needed by the WiMAX stack to be able to cleanup unused mc
groups.
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/netlink/genetlink.c

@@ -225,6 +225,7 @@ void genl_unregister_mc_group(struct genl_family *family,
 	__genl_unregister_mc_group(family, grp);
 	genl_unlock();
 }
+EXPORT_SYMBOL(genl_unregister_mc_group);
 
 static void genl_unregister_mc_groups(struct genl_family *family)
 {