test: fix same socket names in socket-{dgram_data, snd_addr}

Those two tests use same socket name and if both of them are run
simultaneously, they would fight for socket and one will get EADDRINUSE.
This patch gives socket_dgram_data an unique name, so that everyone will
be happy.

travis-ci: success for test: fix same socket names in socket-{dgram_data, snd_addr}
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>

Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>