Restore default port for `adb connect`.

The default port of 5555 was removed a while back, but the help text was
never updated, and other contexts still allow a default port.

Bug: https://issuetracker.google.com/128561172
Test: manual
Change-Id: I6e5e6edeb2243386a0301c0a6cad569189f9910e
diff --git a/socket_spec.cpp b/socket_spec.cpp
index 1333724..98468b5 100644
--- a/socket_spec.cpp
+++ b/socket_spec.cpp
@@ -93,7 +93,7 @@
         }
     } else {
         std::string addr(spec.substr(4));
-        port_value = -1;
+        port_value = DEFAULT_ADB_LOCAL_TRANSPORT_PORT;
 
         // FIXME: ParseNetAddress rejects port 0. This currently doesn't hurt, because listening
         //        on an address that isn't 'localhost' is unsupported.