xfs: introduce xfs_alloc_vextent_near_bno()

The remaining callers of xfs_alloc_vextent() are all doing NEAR_BNO
allocations. We can replace that function with a new
xfs_alloc_vextent_near_bno() function that does this explicitly.

We also multiplex NEAR_BNO allocations through
xfs_alloc_vextent_this_ag via args->type. Replace all of these with
direct calls to xfs_alloc_vextent_near_bno(), too.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
diff --git a/fs/xfs/libxfs/xfs_refcount_btree.c b/fs/xfs/libxfs/xfs_refcount_btree.c
index a980fb1..f3b8609 100644
--- a/fs/xfs/libxfs/xfs_refcount_btree.c
+++ b/fs/xfs/libxfs/xfs_refcount_btree.c
@@ -68,14 +68,13 @@ xfs_refcountbt_alloc_block(
 	args.tp = cur->bc_tp;
 	args.mp = cur->bc_mp;
 	args.pag = cur->bc_ag.pag;
-	args.type = XFS_ALLOCTYPE_NEAR_BNO;
-	args.fsbno = XFS_AGB_TO_FSB(cur->bc_mp, cur->bc_ag.pag->pag_agno,
-			xfs_refc_block(args.mp));
 	args.oinfo = XFS_RMAP_OINFO_REFC;
 	args.minlen = args.maxlen = args.prod = 1;
 	args.resv = XFS_AG_RESV_METADATA;
 
-	error = xfs_alloc_vextent_this_ag(&args);
+	error = xfs_alloc_vextent_near_bno(&args,
+			XFS_AGB_TO_FSB(args.mp, args.pag->pag_agno,
+					xfs_refc_block(args.mp)));
 	if (error)
 		goto out_error;
 	trace_xfs_refcountbt_alloc_block(cur->bc_mp, cur->bc_ag.pag->pag_agno,