core/logging: Fix broken syslog levels on older glibc.

The fix to ASTERISK-25407 introduced the usage of LOG_MAKEPRI. However
this macro is broken in older glibc (< 2.17); it would left-shift the
facility a second time, causing the resultant priority to become
invalid.

The syslog manpage mentions nothing about LOG_MAKEPRI and suggests this:

    The priority argument is formed by ORing the facility and the level
    values [...].

ASTERISK-25510 #close
Reported by: Michael Newton

Change-Id: Ia89debe7fac5ad090c7ef595c0707f31bb1e3d03

main/logger.c

@@ -1514,7 +1514,8 @@ static void logger_print_normal(struct logmsg *logmsg)
 						continue;
 					}
 
-					syslog_level = LOG_MAKEPRI(chan->facility, syslog_level);
+					/* Don't use LOG_MAKEPRI because it's broken in glibc<2.17 */
+					syslog_level = chan->facility | syslog_level; /* LOG_MAKEPRI(chan->facility, syslog_level); */
 					if (!chan->formatter.format_log(chan, logmsg, buf, BUFSIZ)) {
 						syslog(syslog_level, "%s", buf);
 					}