caif: fix a signedness bug in cfpkt_iterate()

The cfpkt_iterate() function can return -EPROTO on error, but the
function is a u16 so the negative value gets truncated to a positive
unsigned short.  This causes a static checker warning.

The only caller which might care is cffrml_receive(), when it's checking
the frame checksum.  I modified cffrml_receive() so that it never says
-EPROTO is a valid checksum.

Also this isn't ever going to be inlined so I removed the "inline".

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/caif/cffrml.c

@@ -84,7 +84,7 @@ static int cffrml_receive(struct cflayer *layr, struct cfpkt *pkt)
 	u16 tmp;
 	u16 len;
 	u16 hdrchks;
-	u16 pktchks;
+	int pktchks;
 	struct cffrml *this;
 	this = container_obj(layr);