Avoid restarting nginx-agent service from pkg on FreeBSD during upgrades

This will end up with a new process being killed immediately by pkg:
https://github.com/freebsd/pkg/blob/1.19.1/libpkg/scripts.c#L100-L103
https://github.com/freebsd/pkg/blob/1.19.1/libpkg/scripts.c#L244-L261

See also:
freebsd/pkg#2128

Author: defanator

scripts/packages/postinstall.sh

@@ -274,6 +274,10 @@ upgrade_config_file() {
 }
 
 restart_agent_if_required() {
+    if [ "${ID}" = "freebsd" ]; then
+        # https://github.com/freebsd/pkg/pull/2128
+        return
+    fi
     if service nginx-agent status >/dev/null 2>&1; then
         printf "PostInstall: Restarting nginx agent\n"
         service nginx-agent restart || true