peek/commit APIs: inconsistent return values in inline docs

[drossetti]

ibv_exp_peer_peek_cq is documented as returning -ENOSPC, while instead it can return ENOSYS & EINVAL & ENOSPC (all positive!)
ibv_exp_peer_commit_qp is documented as returning -ENOSPC, while it can return ENOSYS, -EINVAL and -ENOSPC
mlx5_exp_rollback_send return codes are not documented, while it can return ENOSYS, -ERANGE

browsing the sources, it seems consistent to return positive error codes.

[drossetti]

@ferasd @haggaie it looks like 4.0 still has some problems:

• peer_ops.h still mentions negative error code for both functions
• ibv_exp_peer_commit_qp actually & mlx5_exp_rollback_send returns negative error codes instead of positive