SocketClient: add optional reference counting

Needed to fix a race in netd.

Bug: 3438459
Change-Id: Icd7f5f035510235f733a25c0621479d3e644b152
diff --git a/libsysutils/src/SocketListener.cpp b/libsysutils/src/SocketListener.cpp
index 611d5fe..dde9b55 100644
--- a/libsysutils/src/SocketListener.cpp
+++ b/libsysutils/src/SocketListener.cpp
@@ -55,7 +55,7 @@
     }
     SocketClientCollection::iterator it;
     for (it = mClients->begin(); it != mClients->end();) {
-        delete (*it);
+        (*it)->decRef();
         it = mClients->erase(it);
     }
     delete mClients;
@@ -226,7 +226,7 @@
                 pthread_mutex_unlock(&mClientsLock);
                 /* Destroy the client */
                 close(c->getSocket());
-                delete c;
+                c->decRef();
             }
         }
     }