Fix symbol name for IOCP plugin

Change-Id: I9b212fb192d488643e72ec04d74afe8b56ec5984
Reviewed-on: http://review.couchbase.org/29021
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>