MediaServerConfig: Change methods to const
MediaServerConfig: Change methods to const

Change-Id: I123e6ce495bd18ce95737bca29d88be1e8d3a663

TribeMedia/kms-core,ESTOS/kms-core,ESTOS/kms-core,ESTOS/kms-core,ESTOS/kms-core,Kurento/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,shelsonjava/kms-core,Kurento/kms-core,TribeMedia/kms-core,Kurento/kms-core,TribeMedia/kms-core,shelsonjava/kms-core,TribeMedia/kms-core,Kurento/kms-core