Fix comments in postmaster.c.

Commit 86c23a6eb2 changed the option to specify that postgres will
stop all other server processes by sending the signal SIGSTOP,
from -s to -T. But previously there were comments incorrectly
explaining that SIGSTOP behavior is set by -s option. This commit
fixes them.

Author: Kyotaro Horiguchi
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/20210316.165141.1400441966284654043.horikyota.ntt@gmail.com

src/backend/postmaster/postmaster.c

@@ -3472,7 +3472,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
 			 *
 			 * SIGQUIT is the special signal that says exit without proc_exit
 			 * and let the user know what's going on. But if SendStop is set
-			 * (-s on command line), then we send SIGSTOP instead, so that we
+			 * (-T on command line), then we send SIGSTOP instead, so that we
 			 * can get core dumps from all backends by hand.
 			 */
 			if (take_action)
@@ -3515,7 +3515,7 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
 			 *
 			 * SIGQUIT is the special signal that says exit without proc_exit
 			 * and let the user know what's going on. But if SendStop is set
-			 * (-s on command line), then we send SIGSTOP instead, so that we
+			 * (-T on command line), then we send SIGSTOP instead, so that we
 			 * can get core dumps from all backends by hand.
 			 *
 			 * We could exclude dead_end children here, but at least in the