feat: make smacks_max_unacked_stanzas configurable via env var

Default to 5 (upstream default) when SMACKS_MAX_UNACKED_STANZAS is unset.

Part-of: <http://gitlab.vnc.biz/uxf/vnctalk-prosody/-/merge_requests/3>

config/prosody.cfg.lua.template

@@ -212,7 +212,7 @@ default_archive_policy = "roster"
 --------------------------------------------------------------------------------
 smacks_hibernation_time = ${SMACKS_HIBERNATION_TIME};
 smacks_enabled_s2s = false;
-smacks_max_unacked_stanzas = 5;
+smacks_max_unacked_stanzas = ${SMACKS_MAX_UNACKED_STANZAS};
 smacks_max_ack_delay = 60;
 smacks_max_old_sessions = 10;
 --------------------------------------------------------------------------------

config/startup.sh

@@ -45,6 +45,12 @@ if [ -z "$SMACKS_HIBERNATION_TIME" ]; then
 fi
 export SMACKS_HIBERNATION_TIME
 
+# SMACKS max unacked stanzas. Default 5 (upstream default).
+if [ -z "$SMACKS_MAX_UNACKED_STANZAS" ]; then
+  SMACKS_MAX_UNACKED_STANZAS="5"
+fi
+export SMACKS_MAX_UNACKED_STANZAS
+
 if [ -z "$DEFAULT_JITSI_CONFERENCE" ]; then
   DEFAULT_JITSI_CONFERENCE="conference.jitsi.dev.vnc.de"
   export DEFAULT_JITSI_CONFERENCE