site-python: move to private opnsense dir

Discussed with: @adschellevis

(cherry picked from commit 2a1afe9e)

src/opnsense/scripts/dns/unbound_dhcpd.py

@@ -30,7 +30,7 @@
 """
 import os
 import sys
-sys.path.insert(0, "/usr/local/site-python")
+sys.path.insert(0, "/usr/local/opnsense/site-python")
 import subprocess
 import time
 import tempfile