remove length in ShmSocket ctor, not used.

lichao

2021-06-01 f7f8fbc85c48b003d1e3094a94a3528001977977

 src/defs.cpp

@@ -145,7 +145,7 @@

         auto InitMQ = [&](auto &mq, auto &&id) {
            mq.id_ = id;
            ShmSocket tmp(shm, id, 16);
            ShmSocket tmp(shm, id, eOpenOrCreate);
            mq.offset_ = tmp.AbsAddr();
         };