cifs: Minor Kconfig clarification

Clarify the use of the CONFIG_DFS_UPCALL for DNS name resolution
when server ip addresses change (e.g. on long running mounts)
Signed-off-by: NSteve French <stfrench@microsoft.com>

fs/cifs/Kconfig

@@ -190,8 +190,9 @@ config CIFS_DFS_UPCALL
 	    moves to a different server.  This feature also enables
 	    an upcall mechanism for CIFS which contacts userspace helper
 	    utilities to provide server name resolution (host names to
-	    IP addresses) which is needed for implicit mounts of DFS junction
-	    points. If unsure, say Y.
+	    IP addresses) which is needed in order to reconnect to
+	    servers if their addresses change or for implicit mounts of
+	    DFS junction points. If unsure, say Y.
 
 config CIFS_NFSD_EXPORT
 	  bool "Allow nfsd to export CIFS file system"