Do not modify --bind and --client arguments inplace

Do as iperf_parse_hostname()'s comment says already:  pass a copy of
getopt(3)'s `optarg` aka. to avoid strtok(3) scribbling over `argv[]`.

Otherwise arguments like "fe80::1%vport0" appear as "fe80::1" in the
process list and cause exact matching of process name and arguments
(against what was used) to fail.

OpenBSD's net/iperf3 package ships a rc.subr(8) script and the service
framework uses pgrep(1) to check for running processes, where this
bug causes a mismatch due to the scope identifier being stripped:

```
	$ rcctl get iperf3 flags
	-6 --bind fe80::1%vport0
	$ rcctl check iperf3
	iperf3(failed)
	$ pgrep -fl iperf3
	33091 /usr/local/bin/iperf3 -s -D -6 -B fe80::1
```

Pass a copy to avoid modification, thus fixing rcctl(8) reporting:
```
	$ rcctl check iperf3
	iperf3(ok)
	$ pgrep -fl iperf3
	98863 /usr/local/bin/iperf3 -s -D -6 -B fe80::1%vport0
```

Author: klemensn

src/iperf_api.c

@@ -1289,26 +1289,30 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
                 }
 		iperf_set_test_role(test, 's');
                 break;
-            case 'c':
+            case 'c': {
                 if (test->role == 's') {
                     i_errno = IESERVCLIENT;
                     return -1;
                 }
 		iperf_set_test_role(test, 'c');
 		iperf_set_test_server_hostname(test, optarg);
 
-                if (iperf_parse_hostname(test, optarg, &p, &p1)) {
+                char *arg = strdup(optarg);
+                if (iperf_parse_hostname(test, arg, &p, &p1)) {
 #if defined(HAVE_SO_BINDTODEVICE)
                     /* Get rid of the hostname we saved earlier. */
                     free(iperf_get_test_server_hostname(test));
                     iperf_set_test_server_hostname(test, p);
                     iperf_set_test_bind_dev(test, p1);
 #else /* HAVE_SO_BINDTODEVICE */
+                    free(arg);
                     i_errno = IEBINDDEVNOSUPPORT;
                     return -1;
 #endif /* HAVE_SO_BINDTODEVICE */
                 }
+                free(arg);
                 break;
+            }
             case 'u':
                 set_protocol(test, Pudp);
 		client_flag = 1;
@@ -1441,21 +1445,25 @@ iperf_parse_arguments(struct iperf_test *test, int argc, char **argv)
 		client_flag = 1;
                 break;
 
-            case 'B':
+            case 'B': {
                 iperf_set_test_bind_address(test, optarg);
 
-                if (iperf_parse_hostname(test, optarg, &p, &p1)) {
+                char *arg = strdup(optarg);
+                if (iperf_parse_hostname(test, arg, &p, &p1)) {
 #if defined(HAVE_SO_BINDTODEVICE)
                     /* Get rid of the hostname we saved earlier. */
                     free(iperf_get_test_bind_address(test));
                     iperf_set_test_bind_address(test, p);
                     iperf_set_test_bind_dev(test, p1);
 #else /* HAVE_SO_BINDTODEVICE */
+                    free(arg);
                     i_errno = IEBINDDEVNOSUPPORT;
                     return -1;
 #endif /* HAVE_SO_BINDTODEVICE */
                 }
+                free(arg);
                 break;
+            }
 #if defined (HAVE_SO_BINDTODEVICE)
             case OPT_BIND_DEV:
                 iperf_set_test_bind_dev(test, optarg);