libceph: fix messenger CONFIG_BLOCK dependencies

The ceph messenger has a few spots that are only used when
bio messages are supported, and that's only when CONFIG_BLOCK
is defined.  This surrounds a couple of spots with #ifdef's
that would cause a problem if CONFIG_BLOCK were not present
in the kernel configuration.

This resolves:
    http://tracker.ceph.com/issues/3976

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

include/linux/ceph/messenger.h

@@ -83,9 +83,11 @@ struct ceph_msg {
 	struct list_head list_head;
 
 	struct kref kref;
+#ifdef CONFIG_BLOCK
 	struct bio  *bio;		/* instead of pages/pagelist */
 	struct bio  *bio_iter;		/* bio iterator */
 	int bio_seg;			/* current bio segment */
+#endif /* CONFIG_BLOCK */
 	struct ceph_pagelist *trail;	/* the trailing part of the data */
 	bool front_is_vmalloc;
 	bool more_to_follow;

net/ceph/messenger.c

@@ -9,8 +9,9 @@
 #include <linux/slab.h>
 #include <linux/socket.h>
 #include <linux/string.h>
+#ifdef	CONFIG_BLOCK
 #include <linux/bio.h>
-#include <linux/blkdev.h>
+#endif	/* CONFIG_BLOCK */
 #include <linux/dns_resolver.h>
 #include <net/tcp.h>
 
@@ -2651,9 +2652,11 @@ struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
 	m->page_alignment = 0;
 	m->pages = NULL;
 	m->pagelist = NULL;
+#ifdef	CONFIG_BLOCK
 	m->bio = NULL;
 	m->bio_iter = NULL;
 	m->bio_seg = 0;
+#endif	/* CONFIG_BLOCK */
 	m->trail = NULL;
 
 	/* front */