libceph: fix possible CONFIG_BLOCK build problem

This patch:
    15a0d7b libceph: record message data length
did not enclose some bio-specific code inside CONFIG_BLOCK as
it should have.  Fix that.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

include/linux/ceph/messenger.h

@@ -271,8 +271,10 @@ extern void ceph_msg_data_set_pages(struct ceph_msg *msg, struct page **pages,
 				size_t length, size_t alignment);
 extern void ceph_msg_data_set_pagelist(struct ceph_msg *msg,
 				struct ceph_pagelist *pagelist);
+#ifdef CONFIG_BLOCK
 extern void ceph_msg_data_set_bio(struct ceph_msg *msg, struct bio *bio,
 				size_t length);
+#endif /* CONFIG_BLOCK */
 
 extern struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
 				     bool can_fail);

net/ceph/messenger.c

@@ -817,7 +817,7 @@ static bool ceph_msg_data_bio_advance(struct ceph_msg_data *data, size_t bytes)
 
 	return true;
 }
-#endif
+#endif /* CONFIG_BLOCK */
 
 /*
  * For a page array, a piece comes from the first page in the array
@@ -3011,6 +3011,7 @@ void ceph_msg_data_set_pagelist(struct ceph_msg *msg,
 }
 EXPORT_SYMBOL(ceph_msg_data_set_pagelist);
 
+#ifdef	CONFIG_BLOCK
 void ceph_msg_data_set_bio(struct ceph_msg *msg, struct bio *bio,
 		size_t length)
 {
@@ -3028,6 +3029,7 @@ void ceph_msg_data_set_bio(struct ceph_msg *msg, struct bio *bio,
 	msg->data_length = length;
 }
 EXPORT_SYMBOL(ceph_msg_data_set_bio);
+#endif	/* CONFIG_BLOCK */
 
 /*
  * construct a new message with given type, size