evs.c:
fix defect 477 - header size calculated incorrectly results in assert

BKrev: 42602cf5j6Zi2RZtyz9xB83lZW9R6g


git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@600 fd59a12c-fef9-0310-b244-a6a79926bd2f