changes for pingrecv

Update pingrecv to use ARPQuerier to resolve dest addr.
Remember to point GW at the dest device if using intnet.
update README file

README now explains how to properly run the pingrecv.click
configuration.
update README

explains how to run the corresponding test-ping.click
configuration to work with the pingrecv.click config
Merge pull request #2 from boka808/test_changes

Test changes