Special-case CTL_ALIAS instead of CTL_DNS in udp loopback test.

At the same time remove a bogus test (tested by Jason Wessel).
Quiet some gcc4 warnings from slirp compilation.


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4402 c046a42c-6fe2-441c-8c8c-71466251a162
