ZVOL: Make zvol_inhibit_dev module parameter platform-independent

The module parameter now is represented in FreeBSD sysctls list with
name: 'vfs.zfs.vol.inhibit_dev'. The default value is '0', same as on
Linux side.

Sponsored-by: vStack, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Rob Norris <rob.norris@klarasystems.com>
Signed-off-by: Fedor Uporov <fuporov.vstack@gmail.com>
Closes #17384

module/os/freebsd/zfs/zvol_os.c

@@ -1373,6 +1373,9 @@ zvol_os_create_minor(const char *name)
 	int error;
 	bool replayed_zil = B_FALSE;
 
+	if (zvol_inhibit_dev)
+		return (0);
+
 	ZFS_LOG(1, "Creating ZVOL %s...", name);
 	hash = zvol_name_hash(name);
 	if ((zv = zvol_find_by_name_hash(name, hash, RW_NONE)) != NULL) {

module/os/linux/zfs/zvol_os.c

@@ -1788,9 +1788,6 @@ zvol_fini(void)
 	ida_destroy(&zvol_ida);
 }
 
-module_param(zvol_inhibit_dev, uint, 0644);
-MODULE_PARM_DESC(zvol_inhibit_dev, "Do not create zvol device nodes");
-
 module_param(zvol_major, uint, 0444);
 MODULE_PARM_DESC(zvol_major, "Major number for zvol device");