Use current adb port (if any) for --tcpip

If the current adb port is not 5555 (typically 0 because it is not in
TCP/IP mode), --tcpip automatically executes (among other commands):

    adb tcpip 5555

In case adb was already listening on another port, this command forced
to listen on 5555, and the connection should still succeed.

But this reconfiguration might be inconvenient for the user. If adb is
already in TCP/IP mode, use the current enabled port without
reconfiguration.

Fixes #3591 <https://github.com/Genymobile/scrcpy/issues/3591>

app/src/util/str.h

@@ -6,6 +6,10 @@
 #include <stdbool.h>
 #include <stddef.h>
 
+/* Stringify a numeric value  */
+#define SC_STR(s) SC_XSTR(s)
+#define SC_XSTR(s) #s
+
 /**
  * Like strncpy(), except:
  *  - it copies at most n-1 chars