tests/net: Test network power management awareness

A quick test on a dummy device that:
- opens a socket (success)
- sends data (success)
- suspends (success)
- suspends (failure)
- sends data (failure)
- resumes (success)
- resumes (failure)
- sends data (success)

This permits to show that PM states are properly handled in network
stack.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>