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/net/wireless/mac80211_hwsim.c

@@ -589,7 +589,6 @@ struct hwsim_radiotap_ack_hdr {
 
 /* MAC80211_HWSIM netlinf family */
 static struct genl_family hwsim_genl_family = {
-	.id = GENL_ID_GENERATE,
 	.hdrsize = 0,
 	.name = "MAC80211_HWSIM",
 	.version = 1,