net-test: use None instead of -1 for invalid fds

Test: TreeHugger, UML
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Id82c950ffa568bf05fe32da2285b9692a8b303f3
1 file changed
tree: b3fb6182e39cc5df62b052c5547f4cd8ff254aec
  1. net/
  2. METADATA