refactor(diam): leave SCTP notification length checks to go-sctp
recvSCTPData re-checked each notification's declared length and the
reassembly limit before decoding it. go-sctp's RecvMsg already enforces
both for every notification record it returns, so drop the copies.
recvSCTPData still collects a notification's pieces up to MSG_EOR, which
the small buffers Diameter reads with require, and still returns an
association restart before the data that follows it (RFC 6458 §6, RFC
9260 §5.2.4). Caller-installed notification handlers keep working as
before.
go-sctp's errors reach callers unchanged. Only a receiver other than
go-sctp's could hand recvSCTPData a record that go-sctp rejects; for such
a record the decode error now comes after the record's end instead of an
early length error. The receive tests cover each such input.
Closes #133.
Summary by cubic
Removes recvSCTPData's redundant notification length and reassembly-limit checks, relying on go-sctp's RecvMsg, which already enforces both. For receivers other than go-sctp, a record go-sctp would reject now yields a decode error after the record's end instead of an early length error; arguments go unchanged. Adds receive tests for those cases. Closes #133.