selftests: flip local/remote endpoints in iou-zcrx.py

selftests: flip local/remote endpoints in iou-zcrx.py

The iou-zcrx selftest currently runs the server on the remote host
and the client on the local host. This commit flips the endpoints
such that server runs on localhost and client on remote.
This change brings the iou-zcrx selftest in convention with other
selftests.

Drive-by fix for a missing import exception that happens when the
network interface has less than 2 combined channels.

Test plan: ran iou-zcrx.py selftest between 2 physical machines

Signed-off-by: Vishwanath Seshagiri <vishs@fb.com>
Link: https://patch.msgid.link/20250710165337.614159-1-vishs@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>