Setting Service Bus MaxConcurrentCalls via App Settings in Portal not updating config

#### Investigative information

OS/Plan Info: Linux Function App on Dedicated Plan

#### Repro steps

Provide the steps required to reproduce the problem:

`host.json` has the following settings:

```` json
{
"version": "2.0",
"extensions": {
"serviceBus": {
"prefetchCount": 100,
"messageHandlerOptions": {
"autoComplete": true,
"maxConcurrentCalls": 20,
"maxAutoRenewDuration": "00:05:00"
}
}
}
}
````

In Azure Portal, override `PrefetchCount` and `MaxConcurrentCalls` via app settings:


#### Expected behavior

- `PrefetchCount` updated to 200
- `MaxConcurrentCalls` updated to 35.

#### Actual behavior

- `PrefetchCount` updated to 200 as expected.
- `MaxConcurrentCalls` **is not updated** and remains set at the original value in the `host.json` file.