Fix zpool subcommands error message with some unsupported options

Both 'detach' and 'online' zpool subcommands, when provided with an
unsupported option, forget to print it in the error message:

   # zpool online -t rpool vda3
   invalid option ''
   usage:
      online [-e] <pool> <device> ...

This changes fixes the error message in order to include the actual
option that is not supported.

Reviewed-by: Ryan Moeller <ryan@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #9270

cmd/zpool/zpool_main.c

@@ -6111,9 +6111,8 @@ zpool_do_detach(int argc, char **argv)
 	int ret;
 
 	/* check options */
-	while ((c = getopt(argc, argv, "f")) != -1) {
+	while ((c = getopt(argc, argv, "")) != -1) {
 		switch (c) {
-		case 'f':
 		case '?':
 			(void) fprintf(stderr, gettext("invalid option '%c'\n"),
 			    optopt);
@@ -6342,12 +6341,11 @@ zpool_do_online(int argc, char **argv)
 	int flags = 0;
 
 	/* check options */
-	while ((c = getopt(argc, argv, "et")) != -1) {
+	while ((c = getopt(argc, argv, "e")) != -1) {
 		switch (c) {
 		case 'e':
 			flags |= ZFS_ONLINE_EXPAND;
 			break;
-		case 't':
 		case '?':
 			(void) fprintf(stderr, gettext("invalid option '%c'\n"),
 			    optopt);