MYNEWT-656; kernel/os - fix memory corruption by os_mbuf_copyinto().
diff --git a/kernel/os/src/os_mbuf.c b/kernel/os/src/os_mbuf.c
index 28dec0b..7888a86 100644
--- a/kernel/os/src/os_mbuf.c
+++ b/kernel/os/src/os_mbuf.c
@@ -1086,6 +1086,7 @@
         }
 
         cur = next;
+        cur_off = 0;
     }
 
     /* Append the remaining data to the end of the chain. */