journald: make sure we retain all stream fds across restarts (#6348)

Currently we set 4096 as maximum for number of stream connections that
we accept. However maximum number of file descriptors that systemd is
willing to accept from us is just 1024. This means we can't retain all
stream connections that we accepted. Hence bump the limit of fds in a
unit file so that systemd holds open all stream fds while we are
restarted.

New limit is set to 4224 (4096 + 128).

(cherry picked from commit 3c978ac)

Related: #1359939

units/systemd-journald.service.in

@@ -20,6 +20,7 @@ ExecStart=@rootlibexecdir@/systemd-journald
 Restart=always
 RestartSec=0
 StandardOutput=null
+FileDescriptorStoreMax=4224
 CapabilityBoundingSet=CAP_SYS_ADMIN CAP_DAC_OVERRIDE CAP_SYS_PTRACE CAP_SYSLOG CAP_AUDIT_CONTROL CAP_AUDIT_READ CAP_CHOWN CAP_DAC_READ_SEARCH CAP_FOWNER CAP_SETUID CAP_SETGID CAP_MAC_OVERRIDE
 WatchdogSec=3min