Support end-to-end ECE negotiation in RDMA handshake V3

[chenBright]

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

In #3255, BringUpQp() only did a local ibv_query_ece + ibv_set_ece
roundtrip and never exchanged ECE capabilities with the peer.

What is changed and the side effects?

Changed:

This PR implements an end-to-end ECE negotiation in the v3 handshake.

• Client (RdmaHandshakeClientV3::SendLocalHello): query local ECE,
  store it in _outgoing_ece, advertise it in the v3 hello.
• Server (BringUpQp): apply the client's ECE during INIT->RTR (ibv_set_ece).
  After QP reaches RTS, ibv_query_ece to obtain the reduced/negotiated ECE
  (the subset both peers support) and store it in _outgoing_ece.
• Server (SendLocalHello → FillLocalRdmaHello): advertise the negotiated ECE
  in the reply hello.
• Client (BringUpQp): apply the server's reduced ECE during INIT->RTR.

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull request overview

This PR adds end-to-end ECE (Enhanced Connection Establishment) negotiation to the RDMA handshake v3 (“RDM3”), so client/server exchange ECE capabilities and apply the negotiated (reduced) result during QP bring-up, while gracefully degrading when ECE isn’t supported.

Changes:

• Extend the v3 protobuf handshake (RdmaHello) to optionally carry ECE capabilities/negotiated results.
• Implement role-specific ECE handling: client queries+advertises local ECE; server applies client ECE during INIT→RTR, then queries and advertises negotiated ECE after RTS; client applies server’s negotiated ECE.
• Make ibv_query_ece/ibv_set_ece optional dynamic symbols and add unit tests + broaden CI test execution.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/brpc_rdma_unittest.cpp	Adds v3 handshake tests covering ECE presence/absence and server behavior with ECE-enabled/disabled.
src/brpc/rdma/rdma_helper.cpp	Loads ECE verbs symbols optionally so older libibverbs can still run RDMA without failing init.
src/brpc/rdma/rdma_handshake.proto	Adds RdmaEce and an optional ece field in RdmaHello for v3 negotiation.
src/brpc/rdma/rdma_handshake.h	Extends parsed hello to carry optional ibv_ece for v3.
src/brpc/rdma/rdma_handshake.cpp	Adds FLAGS_rdma_ece, advertises/parses ECE in v3 hello, and queries local ECE on the v3 client.
src/brpc/rdma/rdma_endpoint.h	Stores _outgoing_ece to advertise role-specific ECE in the next hello.
src/brpc/rdma/rdma_endpoint.cpp	Updates QP bring-up to accept parsed hello (incl. optional ECE) and queries negotiated ECE on the server after RTS.
.github/workflows/ci-linux.yml	Runs the full //test/... suite under the RDMA Bazel config (removes previous gtest filter).

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