config, logging: correct the logging parameters (#856)

The logging parameters were listing using uppercase, which is wrong. 

According to multus configuration, they should be in camelCase - [0] and [1].

[0] - https://github.com/k8snetworkplumbingwg/multus-cni/blob/779170a48ea767fe367f58ca472a8c403c203c6f/pkg/types/types.go#L45
[1] - https://github.com/k8snetworkplumbingwg/multus-cni/blob/779170a48ea767fe367f58ca472a8c403c203c6f/pkg/types/types.go#L46

docs/configuration.md

@@ -110,7 +110,7 @@ Optionally, you may have Multus log to a file on the filesystem. This file will
 For example in your CNI configuration, you may set:
 
 ```
-    "LogFile": "/var/log/multus.log",
+    "logFile": "/var/log/multus.log",
 ```
 
 #### Logging Level
@@ -127,7 +127,7 @@ The available logging level values, in decreasing order of verbosity are:
 You may configure the logging level by using the `LogLevel` option in your CNI configuration. For example:
 
 ```
-    "LogLevel": "debug",
+    "logLevel": "debug",
 ```
 
 #### Logging Options