rtnetlink: Compute and store minimum ifinfo dump size

The message size allocated for rtnl ifinfo dumps was limited to
a single page.  This is not enough for additional interface info
available with devices that support SR-IOV and caused a bug in
which VF info would not be displayed if more than approximately
40 VFs were created per interface.

Implement a new function pointer for the rtnl_register service that will
calculate the amount of data required for the ifinfo dump and allocate
enough data to satisfy the request.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

net/ipv4/ipmr.c

@@ -2544,7 +2544,8 @@ int __init ip_mr_init(void)
 		goto add_proto_fail;
 	}
 #endif
-	rtnl_register(RTNL_FAMILY_IPMR, RTM_GETROUTE, NULL, ipmr_rtm_dumproute);
+	rtnl_register(RTNL_FAMILY_IPMR, RTM_GETROUTE,
+		      NULL, ipmr_rtm_dumproute, NULL);
 	return 0;
 
 #ifdef CONFIG_IP_PIMSM_V2