add missing string.h include

diff --git a/src/msgb.c b/src/msgb.c
index f039be0..ce390e8 100644
--- a/src/msgb.c
+++ b/src/msgb.c
@@ -19,6 +19,7 @@
 
 
 #include <unistd.h>
+#include <string.h>
 #include <stdlib.h>
 #include <sys/types.h>