astlpc: Introduce protocol v3 with integrity checks

v3 of the binding adds a CRC-32 value as a medium-specific trailer to
each packet passing over the binding interface.

The patch includes a naive bit-shift implementation of CRC-32, we can
improve it later as necessary.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I93a95bccef30010d56e10e29b6d84554268ab7af
diff --git a/libmctp.h b/libmctp.h
index 36e1483..46bda90 100644
--- a/libmctp.h
+++ b/libmctp.h
@@ -59,6 +59,7 @@
 void *mctp_pktbuf_alloc_start(struct mctp_pktbuf *pkt, size_t size);
 void *mctp_pktbuf_alloc_end(struct mctp_pktbuf *pkt, size_t size);
 int mctp_pktbuf_push(struct mctp_pktbuf *pkt, void *data, size_t len);
+void *mctp_pktbuf_pop(struct mctp_pktbuf *pkt, size_t len);
 
 /* MCTP core */
 struct mctp;