Make SctpDataChannel::Send return false with any error. Update the comments and tests accordingly.

Prior to this change, false is returned upon INVALID_STATE or RESOURCE_EXHAUSTED. Upon other errors such as NETWORK_ERROR and INVALID_RANGE(i.e. a message exceeding socket limit), true is returned but the message is not sent anyways. This renders the return value less useful for application developers using data channel.

Per RFC883, a data channel must provide message fragmentation support such that IP-layer fragmentation can be avoided no matter how large a message the JavaScript application passes to be sent. Further changes are needed for SctpDataChannel::Send to be compliant.

Bug: webrtc:406012421
Change-Id: I9c9b6f719b76b665a0b3a8e9af0f76f2d97e234a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/427800
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46459}