Fix coverity warnings in VOM and VAPI

Change-Id: I0db55e079f9b1835668c8efe69e6e6f7f8437b00
Signed-off-by: Neale Ranns <neale.ranns@cisco.com>
diff --git a/src/vpp-api/vapi/vapi_internal.h b/src/vpp-api/vapi/vapi_internal.h
index 2c51c67..e9a9726 100644
--- a/src/vpp-api/vapi/vapi_internal.h
+++ b/src/vpp-api/vapi/vapi_internal.h
@@ -90,8 +90,8 @@
   const char *name_with_crc;
   size_t name_with_crc_len;
   bool has_context;
-  int context_offset;
-  int payload_offset;
+  unsigned int context_offset;
+  unsigned int payload_offset;
   size_t size;
   generic_swap_fn_t swap_to_be;
   generic_swap_fn_t swap_to_host;