[DLM] Fix uninitialised variable in receiving

The length of the second element of the kvec array was not initialised before
being added to the first one. This could cause invalid lengths to be passed to
kernel_recvmsg

Signed-Off-By: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>