net/slirp: Tell the users when they are using deprecated options

We don't want to support the legacy -tftp, -bootp, -smb and
-net channel options forever. So let's start telling the users
that they are deprecated and what option should be used instead.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/slirp.c

@@ -784,6 +784,9 @@ int net_slirp_parse_legacy(QemuOptsList *opts_list, const char *optarg, int *ret
         return 0;
     }
 
+    error_report("The '-net channel' option is deprecated. "
+                 "Please use '-netdev user,guestfwd=...' instead.");
+
     /* handle legacy -net channel,port:chr */
     optarg += strlen("channel,");