Add missing include headers for compilation on x86 targets.

Change-Id: I99f7b79bfb5b6305a0772f418a54ace50cac1bbe
diff --git a/PppController.cpp b/PppController.cpp
index f508f4e..4caf382 100644
--- a/PppController.cpp
+++ b/PppController.cpp
@@ -17,6 +17,7 @@
 #include <stdlib.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <string.h>
 
 #include <sys/socket.h>
 #include <sys/stat.h>