syslog: revert LOG_FAC/LOG_FACMASK changes

commit 895736d49bd2bb318c69de99a05ea70c035c2da9 made these changes
along with fixing a real bug in LOG_MAKEPRI. based on further
information, they do not seem to be well-motivated or in line with
policy.

the result of LOG_FAC is not a meaningful facility value if we shift
it down like before, but apparently the way it is used by applications
is as an index into an array of facility names. moreover, all
historical systems which define it do so with the shift. as it is a
nonstandard interface, there is no justification for providing a macro
by the same name that is incompatible with historical practice.

the value of LOG_FACMASK likewise is 0x3f8 on all historical systems
checked. while only 5 bits are used for existing facility codes, the
convention seems to be that all 7 bits belong to the facility field
and theoretically could be used to expand to having more facilities.
that seems unlikely to happen, but there is no reason to make a
gratuitously incompatible change here.

include/syslog.h

@@ -46,8 +46,8 @@ extern "C" {
 #define LOG_LOCAL7   (23<<3)
 
 #define LOG_NFACILITIES 24
-#define LOG_FACMASK 0xf8
-#define LOG_FAC(p) ((p)&LOG_FACMASK)
+#define LOG_FACMASK 0x3f8
+#define LOG_FAC(p) (((p)&LOG_FACMASK)>>3)
 
 #define LOG_PID    0x01
 #define LOG_CONS   0x02

src/misc/syslog.c

@@ -128,7 +128,7 @@ static void _vsyslog(int priority, const char *message, va_list ap)
 static void __vsyslog(int priority, const char *message, va_list ap)
 {
 	int cs;
-	if (!(log_mask & LOG_MASK(priority&7)) || (priority&~0xff)) return;
+	if (!(log_mask & LOG_MASK(priority&7)) || (priority&~0x3ff)) return;
 	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 	LOCK(lock);
 	_vsyslog(priority, message, ap);