Fix SDP session ID length limitation

[lo-simon]

According to the RFC 4566 5.2. Origin

<sess-id> is a numeric string such that the tuple of <username>,
 
<sess-id>, <nettype>, <addrtype>, and <unicast-address> forms a
 
globally unique identifier for the session.  The method of
 
<sess-id> allocation is up to the creating tool, but it has been
 
suggested that a Network Time Protocol (NTP) format timestamp be
 
used to ensure uniqueness [[13](https://datatracker.ietf.org/doc/html/rfc4566#ref-13)].

The current implementation limit for the session ID is UINT64_MAX (18446744073709551615), i.e., its maximum length is 20 digits. To fulfill the RFC above, the string should not be limited in length.

[garethsb]

This is at the least incomplete since the same argument applies to sess-version.

[lo-simon]

This is at the least incomplete since the same argument applies to sess-version.

Well spotted @garethsb. Will extend the change to sess-version.