At least on Linux, when process A connects to process B over a Unix
domain socket, unless process A bound its socket to a name before
it made the connection, process B gets an empty peer name.  Until
now, OVS has just reported the name of the connection as "unix".
This is not meaningful, of course.  I do not know of a good general
solution to this problem, but this commit attempts a step in the
right direction by at least giving each connection of this kind a
number: "unix#1", "unix#2", and so on.  That way, in log messages
one can at least see which messages are related to a particular
connection.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Justin Pettit <jpettit@ovn.org>