unix: SockaddrVM uses "context ID" terminology instead of "client ID"

"When the client creates a connection, instead of providing an IP address
to choose its server, the client must provide the context ID (CID) of a
virtual machine or host."
Reference:
https://pubs.vmware.com/vsphere-60/topic/com.vmware.ICbase/PDF/ws9_esx60_vmci_sockets.pdf

Change-Id: Ia2dfe015594e0ca43a3c8acec1f43d418f5781af
Reviewed-on: https://go-review.googlesource.com/37864
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed