[FIX] payment_*: multiwebsite base_url

Fine-tunning of 937b5c07

Have a multiwebsite setup
have a payment installed for one of the two websites

Make an order on that website and try to pay

Before this commit, the transaction doesn't come back to odoo's
payment success controller
This was because the return url was set to the web base url ICP

After this commit, the payment success page is opened as we took
the request's url as the return url

opw-2080352

closes odoo/odoo#39587

Signed-off-by: Jorge Pinna Puissant (jpp) <jpp@odoo.com>