vcl: fix event triggered after closing connections.
vcl: fix event triggered after closing connections.

Improve the accuracy of epoll event(EPOLLRDHUP).

Type: fix

Signed-off-by: liuyacan <12ac68815e324e48eabd4f40bba5a7fc8ec28656@corp.netease.com>
Change-Id: Ia31e696a0666c417ca99e684c6a4515f1cafc646

chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp