sip utils: include memory

Change-Id: I54fd4ec72846635f325f583abc8afb8a027d453c
diff --git a/src/sip_utils.h b/src/sip_utils.h
index 25b2a2e..67238fa 100644
--- a/src/sip_utils.h
+++ b/src/sip_utils.h
@@ -22,6 +22,7 @@
 #include <string>
 #include <vector>
 #include <cstring> // strcmp
+#include <memory>
 
 #include <pjsip/sip_msg.h>
 #include <pjlib.h>