SIP UDP too long

I did a turn-up with a Verizon hosted service tonight and ran into too large of packets.  My initial invite was fine...but once they gave me a 401 unauthorized, gave me the info I needed to send back for authentication....that took me up to about 1593 bytes.    Verizon's SBC seems to have the default 1500 byte limit and they weren't willing to budge.

This is an existing deployment and I added some sites to it using child realms.  This seemed to add a "DMR" and another header.  I was able to strip those out by removing some sip-config options.    This wasn't enough....I remove the "route" header with a sip-manipulation....and this got me down to 1471 bytes.   That's still pretty close for comfort.   A few extra digits in a phone number....or a long CID name could push me over 1500.