sdpagent: Minimize usage of SdpMessageContext which is expected to be deprecated in due time
sdpagent: Minimize usage of SdpMessageContext which is expected to be deprecated in due time

Change-Id: I745c7a6db206d992f3c644c35620ac3842ce5f6e

Kurento/kms-core,Kurento/kms-core,ESTOS/kms-core,ESTOS/kms-core,Kurento/kms-core,ESTOS/kms-core,Kurento/kms-core,ESTOS/kms-core