Update sip-trunk.mdx

Author: sahilsuman933

fern/advanced/sip/sip-trunk.mdx

@@ -12,6 +12,7 @@ To allow SIP signaling and media between Vapi and your SIP provider, you must al
 
 - 44.229.228.186/32
 - 44.238.177.138/32
+- 172.31.9.106/32
 
 These IPs are used exclusively for SIP traffic.