bug 1561697: add mozilla::ipc::WriteIPDLParam to prefix list

This adds mozilla::ipc::WriteIPDLParam to the prefix list so signature
generation continues beyond it. By itself, it's too general a bucket.  It'd
help to know what the T actually is, but that breaks normalization.  Continuing
to the next frame should clarify the bucket.

socorro/signature/siglists/prefix_signature_re.txt

@@ -121,6 +121,7 @@ mozilla::ipc::RPCChannel::Call
 mozilla::ipc::RPCChannel::CxxStackFrame::CxxStackFrame
 mozilla::ipc::RPCChannel::EnteredCxxStack
 mozilla::ipc::RPCChannel::Send
+mozilla::ipc::WriteIPDLParam
 mozilla::layers::CompositorD3D11::Failed
 mozilla::layers::CompositorD3D11::HandleError
 mozilla::SpinEventLoopUntil<T>