pgsql: Initialize ListenSocket array earlier.

Initialize ListenSocket array earlier.

After commit b0bea38705, syslogger prints 63 warnings about failing to
close a listen socket at postmaster startup. That's because the
syslogger process forks before the ListenSockets array is initialized,
so ClosePostmasterPorts() calls "close(0)" 64 times. The first call
succeeds, because fd 0 is stdin.

This has been like this since commit 9a86f03b4e in version 13, which
moved the SysLogger_Start() call to before initializing ListenSockets.
We just didn't notice until commit b0bea38705 added the LOG message.

Reported by Michael Paquier and Jeff Janes.

Author: Michael Paquier
Discussion: https://www.postgresql.org/message-id/ZOvvuQe0rdj2slA9%40paquier.xyz
Discussion: https://www.postgresql.org/message-id/ZO0fgDwVw2SUJiZx@paquier.xyz#482670177eb4eaf4c9f03c1eed963e5f
Backpatch-through: 13

Branch
------
REL_16_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/5f38ff3d0f65b7d092362aaf7375cce050a13bba

Modified Files
--------------
src/backend/postmaster/postmaster.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)