syslogd: Improve handling of configuration errors

Make parse_selector() print a warning to stderr and continue parsing the
config if it encounters an invalid facility or priority.  Note that
because the parsing is done from a casper service, there isn't a good
mechanism to log errors; the warnings are visible only when syslogd is
started in debug mode.

Reported by:	Doug Hardie <bc979@lafn.org>
MFC after:	1 week
Fixes:		f4b4a10abb ("syslogd: Move selector parsing into its own function")
Reviewed by:	jfree, jlduran, eugen, delphij
Differential Revision:	https://reviews.freebsd.org/D55033

usr.sbin/syslogd/syslogd.c

@@ -2932,8 +2932,9 @@ parse_selector(const char *p, struct filed *f)
 
 		pri = decode(buf, prioritynames);
 		if (pri < 0) {
-			dprintf("unknown priority name \"%s\"", buf);
-			return (NULL);
+			warnx("unknown priority name \"%s\", setting to 'info'",
+			    buf);
+			pri = LOG_INFO;
 		}
 	}
 	if (!pri_cmp)
@@ -2955,11 +2956,12 @@ parse_selector(const char *p, struct filed *f)
 		} else {
 			i = decode(buf, facilitynames);
 			if (i < 0) {
-				dprintf("unknown facility name \"%s\"", buf);
-				return (NULL);
+				warnx("unknown facility name \"%s\", ignoring",
+				    buf);
+			} else {
+				f->f_pmask[i >> 3] = pri;
+				f->f_pcmp[i >> 3] = pri_cmp;
 			}
-			f->f_pmask[i >> 3] = pri;
-			f->f_pcmp[i >> 3] = pri_cmp;
 		}
 		while (*p == ',' || *p == ' ')
 			p++;