vcl: fix error state switch for VCL_STATE_LISTEN_NO_MQ sessions

vcl: fix error state switch for VCL_STATE_LISTEN_NO_MQ sessions

When a VCL_STATE_LISTEN_NO_MQ session receives an ACCEPTED message,
but then receives either a RESET or DISCONNECTED message from VPP
before the session is unlistened, the listen session state is
switched to DISCONNECT.
The subsequent CLEANUP message handler attempts to send a reset
reply message to VPP, but since the vpp_evt_q for the listen
session is null, this leads to a crash.

Type: fix
Change-Id: Id7e88dcb16df3eda912b3f763730ec8d8973473a
Signed-off-by: wanghanlin <wanghanlin@corp.netease.com>