[backport#14790] Tests: Allow running rpc_bind.py --nonloopback test without IPv6

Summary:
c9066f07c94e3610f7762d6406851cd135790511 Allow running rpc_bind.py --nonloopback test without IPv6 (Kristaps Kaupe)

Pull request description:

Don't see a reason why this can't be tested with IPv4 only.

Depends on D8133

Backport of Core PR14790

Test Plan:

ninja all
test_runner.py rpc_bind

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D8134