added vxlan & NSH context decode to service_function.py
moved service index processing to nsh_service_index.py
added a check for service index 0

Change-Id: If85fb64487f9a1700cc17699164317e69522632d
Signed-off-by: Jim Guichard <jguichar@cisco.com>
updated service_function.py to pass server_base_values
updated nsh_service_index.py to receive server_base_values as parameter

Change-Id: I94b384000b6d76279cf40441c6344394557cea67
Signed-off-by: Jim Guichard <jguichar@cisco.com>