sysutils: add missing <vector> include

Upgrading to clang-r522817's new libc++ requires that <vector> be
included here.

Bug: 333165689
Test: treehugger
Flag: EXEMPT, fix build error
Change-Id: Ib9a072ddb39477b98c79879da6354557695ba350
diff --git a/libsysutils/include/sysutils/SocketListener.h b/libsysutils/include/sysutils/SocketListener.h
index 67a691a..a7fd09e 100644
--- a/libsysutils/include/sysutils/SocketListener.h
+++ b/libsysutils/include/sysutils/SocketListener.h
@@ -19,6 +19,7 @@
 #include <pthread.h>
 
 #include <unordered_map>
+#include <vector>
 
 #include <sysutils/SocketClient.h>
 #include "SocketClientCommand.h"