qapi-schema: mark InetSocketAddress as mandatory again

Revert the qapi-schema.json change done in:

  commit 0983f5e6
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Tue Sep 1 14:46:50 2015 +0100

    sockets: allow port to be NULL when listening on IP address

Switching "port" from mandatory to optional causes the QAPI
code generator to add a 'has_port' field to the InetSocketAddress
struct. No code that created InetSocketAddress objects was updated
to set 'has_port = true', which caused the non-NULL port strings
to be silently dropped when copying InetSocketAddress objects.

Reported-by: Knut Omang <knuto@ifi.uio.no>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1445509543-30679-1-git-send-email-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>