4.2bsd ts driver allows O_RDWR without write ring +FIX

[Don Speck]

Index:		sys/vaxuba/ts.c  4.2  Fix
Description:	The TS11/TU80 driver allows opens with mode O_RDWR
		even if there's no write ring.	All the other tape
		drivers require a write ring for O_RDWR mode.
Repeat-by:	Load a tape without write ring, open the drive for
		reading and writing, and try writing.  The open
		will succeed but the writes will fail (errno=EIO).
Fix:

diff old/ts.c ts.c
184c184
<	if ((flag&(FREAD|FWRITE)) == FWRITE && (sc->sc_sts.s_xs0&TS_WLK)) {
---
>	if ((flag&FWRITE) && (sc->sc_sts.s_xs0&TS_WLK)) {