dcsctp: Fix incorrect comparison in FullStreamId

The original code implements the comparison incorrectly, which violates
the strict weak ordering required for keys in a std::map.

This change fixes the implementation by using `std::tie` to perform a
correct lexicographical comparison, which is the idiomatic C++ approach.

Bug: webrtc:5696
Change-Id: I2a5d836b10d536d14ccd544b8b8b306535148c96
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/407880
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Jonas Oreland <jonaso@webrtc.org>
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45559}