Update *alter_sessions action

Will now support two extra parameters: address and codec. For *internal
connections, the birpc.Service object will be retrieved from rpcParamsMap
from utils. Supported codecs: <*gob|*json|*http_jsonrpc> (ingored for
*internal address).

Action does not bother with setting defaults anymore, lets the API
handle them.

Improve action comments.

Add unit tests for the action. UnregisterRpcParams' implementation was
required.

Updated *alter_sessions action tariffplan for radius coa integration test
to include address and codec.

Some birpc clients that are set up in integration tests were still registering
a SessionSv1 object. Updated them to register an AgentV1 object instead.

analyzers/analyzers_it_test.go

@@ -123,7 +123,7 @@ func testAnalyzerSStartEngine(t *testing.T) {
 
 // Connect rpc client to rater
 func testAnalyzerSRPCConn(t *testing.T) {
-	srv, err := birpc.NewService(new(smock), utils.SessionSv1, true)
+	srv, err := birpc.NewService(new(smock), utils.AgentV1, true)
 	if err != nil {
 		t.Fatal(err)
 	}