Add missing headers for compilation on x86 targets

Change-Id: I5f4dc797b353a0f01fa00d38375ec303bf863254
diff --git a/libnetutils/dhcp_utils.c b/libnetutils/dhcp_utils.c
index cb0960f..f02a44a 100644
--- a/libnetutils/dhcp_utils.c
+++ b/libnetutils/dhcp_utils.c
@@ -18,6 +18,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <arpa/inet.h>
 #include <netinet/in.h>