--Edited --
Hi William,
This option is available in x8.8 as per an internal bug. VCS x8.8 includes a way to select the TLS version to be used in SIP communications. Please log in via SSH (with PUTTY) and try the command
xConfiguration SIP Advanced SipTlsVersions ?
It will offer the options ( TLSv1.1:TLSv1.2)
HTH
Manish