A configmap is not bound to a host (multiple pods on different hosts can share the same configmap). But you can get details in a running pod. You can get the host IP the following way in an environment variable. Add the following in your pods spec section:

env:
- name: MY_NODE_IP
  valueFrom:
    fieldRef:
      fieldPath: status.hostIP

Details about passing other values to env vars can be found in the official documentation.

Unfortunately you can't get the hostIP in a volume, as the downwardAPI doesn't have access to status.hostIP (docu)