utils/ipc-inject: Don't inject messages with header

utils/ipc-inject: Don't inject messages with header

When ipc-inject injects a message, it uses ipc_endpoint_publish()
to re-publish it in its entirety, including the wrapper it was
received in, causing it to be double-wrapped.

This commit modifies ipc-inject so that it re-publishes only the
data of the received message, instead of the entire message.