afs: Read of file returns EBADMSG

A read of a large file on an afs mount failed:

# cat junk.file > /dev/null
cat: junk.file: Bad message

Looking at the trace, call->offset wrapped since it is only an unsigned short. In afs_extract_data:

        _enter("{%u},{%zu},%d,,%zu", call->offset, len, last, count);

...

        if (call->offset < count) {
                if (last) {
                        _leave(" = -EBADMSG [%d < %zu]", call->offset, count);
                        return -EBADMSG;
                }

Which matches the trace:

[cat ] ==> afs_extract_data({65132},{524},1,,65536)
[cat ] <== afs_extract_data() = -EBADMSG [0 < 65536]

call->offset went from 65132 to 0. Fix this by making call->offset an unsigned int.

---

Index: linux-build/fs/afs/internal.h
===================================================================
@@ -109,7 +109,7 @@ struct afs_call {
 	unsigned		reply_size;	/* current size of reply */
 	unsigned		first_offset;	/* offset into mapping[first] */
 	unsigned		last_to;	/* amount of mapping[last] */
-	unsigned short		offset;		/* offset into received data store */
+	unsigned		offset;		/* offset into received data store */
 	unsigned char		unmarshall;	/* unmarshalling phase */
 	bool			incoming;	/* T if incoming call */
 	bool			send_pages;	/* T if data from mapping should be sent */