Fix cannot setup IPAM gateway

[qnap-ericfan]

What I did
Here is my docker-compose-yaml

services:
  test:
    image: nginx
    networks:
      - br-test

networks:
  br-test:
    driver: bridge
    ipam:
      config:
        - subnet: 172.17.4.0/24
          gateway: 172.17.4.1

I execute command docker-compose up, then I inspect br-test network.
But IPAM gateway doesn't be setup correctly.

[
    {
       ...
        "IPAM": {
            "Driver": "default",
            "Config": [
                {
                    "Subnet": "172.17.4.0/24"
                }
            ]
        }
        ...
    }
]

Related issue
fixes #9330

(not mandatory) A picture of a cute animal, if possible in relation with what you did

[blop]

@qnap-ericfan Thank you for the PR !
I have the same issue, hope this get merged soon ;-)

I'll try to build from your branch in the meantime.

[blop]

Related to #8742 and #9330

[gaby]

Hopefully this gets merged... We are still stuck in v1.29 because of IPAM issues.

[potiuk]

Would be GREAT!

[gaby]

@ndeloof @gtardif @ulyssessouza @rumpl Can someone take a look at this PR. Without proper IPAM support it's impossible to migrate to docker-compose v2 Thanks!

[ulyssessouza]

Lgtm