test: switch from deprecated /var/run to /run

  The FHS 3.0 [F] has deprecated /var/run in favor of /run. Current
  distributions have done so for a long time (for example in Debian
  since 6.0 “squeeze”), even though they provide a compatibility
  symlink from /var/run to /run. But software like systemd have
  started emitting warnings when using /var/run, for example for
  its PIDFile directive, which pollutes the logs.

test/unit/7.cfg

@@ -181,7 +181,7 @@ modparam("nathelper", "sipping_method", "OPTIONS")
 modparam("nathelper", "received_avp", "$avp(i:801)")
 
 loadmodule "rtpproxy/rtpproxy.so"
-modparam("rtpproxy", "rtpproxy_sock", "unix:/var/run/rtpproxy.sock")
+modparam("rtpproxy", "rtpproxy_sock", "unix:/run/rtpproxy.sock")
 modparam("rtpproxy", "rtpproxy_disable_tout", 60)
 modparam("rtpproxy", "rtpproxy_tout", 1)
 modparam("rtpproxy", "rtpproxy_retr", 5)