Initialize tcpip process before resolver process.

Since introduction of mDNS (https://github.com/contiki-os/contiki/commit/f145c17039b778cde1d53b6828757cd91dc8480a)
the resolver process initialization depends on the tcpip process
already being initialized (because of the call to udp_new()).
Merge pull request #346 from oliverschmidt/master

Initialize tcpip process before resolver process.