genetlink: no longer support using static family IDs

Static family IDs have never really been used, the only
use case was the workaround I introduced for those users
that assumed their family ID was also their multicast
group ID.

Additionally, because static family IDs would never be
reserved by the generic netlink code, using a relatively
low ID would only work for built-in families that can be
registered immediately after generic netlink is started,
which is basically only the control family (apart from
the workaround code, which I also had to add code for so
it would reserve those IDs)

Thus, anything other than GENL_ID_GENERATE is flawed and
luckily not used except in the cases I mentioned. Move
those workarounds into a few lines of code, and then get
rid of GENL_ID_GENERATE entirely, making it more robust.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/scsi/pmcraid.c

@@ -1369,12 +1369,6 @@ static struct genl_multicast_group pmcraid_mcgrps[] = {
 };
 
 static struct genl_family pmcraid_event_family = {
-	/*
-	 * Due to prior multicast group abuse (the code having assumed that
-	 * the family ID can be used as a multicast group ID) we need to
-	 * statically allocate a family (and thus group) ID.
-	 */
-	.id = GENL_ID_PMCRAID,
 	.name = "pmcraid",
 	.version = 1,
 	.maxattr = PMCRAID_AEN_ATTR_MAX,