fix: handle consul nil port cases by defaulting to port 80

[oil-oil]

Description

When using consul as a service registry, if a user registers a service without filling in the port number, the default value is not set in apisix, resulting in svc_port possibly being nil, which in turn results in local service_id = svc_address ... “:” ... svc_port cannot be spliced.

Which issue(s) this PR fixes:

Fixes https://github.com/apache/apisix/issues/11134

Checklist

• [x] I have explained the need for this PR and the problem it solves
• [x] I have explained the changes or the new features added to this PR
• [x] I have added tests corresponding to this change
• [ ] I have updated the documentation to reflect this change
• [ ] I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)