Correct coding style in decode-ethernet.c

This file is given as the example of correct coding style, so make sure it
follows the coding standard.

Shorted one line >80 characters
Put function { on following line.

Passes regression test:
https://buildbot.suricata-ids.org/builders/ken-tilera/builds/88
https://buildbot.suricata-ids.org/builders/ken-tilera-pcap/builds/22