nfs: fix PNFS_FLEXFILE_LAYOUT Kconfig default

This follows what was done in 8c2fabc6.
With the default being m, it's impossible to build the module into the
kernel.
Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/Kconfig

@@ -127,7 +127,7 @@ config PNFS_BLOCK
 config PNFS_FLEXFILE_LAYOUT
 	tristate
 	depends on NFS_V4_1 && NFS_V3
-	default m
+	default NFS_V4
 
 config NFS_V4_1_IMPLEMENTATION_ID_DOMAIN
 	string "NFSv4.1 Implementation ID Domain"