quick fix XmppService for eventService.handleOadrPayload()

This is quick fix XmppService for eventService.handleOadrPayload().

I noticed that current application does not process any posted xmpp messages.
This problem was caused by NPE when calling eventService.handleOadrPayload() in XmppService.java, method oadrPacketListener().
The class static variable "eventService" seems initiated by @Inject, but this injection does not work.
I modified code with using EiEventService.getInstance() instead of @Inject.

Again, this is quick fix to see how this application works with posted xmpp message.
The injection failure should be investigated, though.