adb: Distinguish betwen already-connected and connection failure

This change returns a different value (-EALREADY) when a connection has
already been established, as opposed to a real connection failure (which
still returns -1).

Bug: 74411879
Test: Opened a socket, tried to adb connect to it,
      got "failed to connect to localhost:1337"

Change-Id: Ic216ddef7f28eb43ca750f9e51d068c077d54b07
diff --git a/adb/transport.cpp b/adb/transport.cpp
index 92c52e2..f5f6d26 100644
--- a/adb/transport.cpp
+++ b/adb/transport.cpp
@@ -974,7 +974,7 @@
             VLOG(TRANSPORT) << "socket transport " << transport->serial
                             << " is already in pending_list and fails to register";
             delete t;
-            return -1;
+            return -EALREADY;
         }
     }
 
@@ -983,7 +983,7 @@
             VLOG(TRANSPORT) << "socket transport " << transport->serial
                             << " is already in transport_list and fails to register";
             delete t;
-            return -1;
+            return -EALREADY;
         }
     }
 
diff --git a/adb/transport_local.cpp b/adb/transport_local.cpp
index c09fcb7..8032421 100644
--- a/adb/transport_local.cpp
+++ b/adb/transport_local.cpp
@@ -101,7 +101,11 @@
     int ret = register_socket_transport(fd, serial.c_str(), port, 0);
     if (ret < 0) {
         adb_close(fd);
-        *response = android::base::StringPrintf("already connected to %s", serial.c_str());
+        if (ret == -EALREADY) {
+            *response = android::base::StringPrintf("already connected to %s", serial.c_str());
+        } else {
+            *response = android::base::StringPrintf("failed to connect to %s", serial.c_str());
+        }
     } else {
         *response = android::base::StringPrintf("connected to %s", serial.c_str());
     }