UE: add PCO in PDN Connectivity Request message

Add the PCO so that MME allocates the IP address
accordingly. The protocol ID known as "IP address
allocation via NAS signalling" is assigned.

Otherwise, the OAI UE will always has IP address
set to 0.0.0.0

This has tested with OAI eNB with S1 interface using
OAI EPC.

Reference:
http://www.sharetechnote.com/html/Handbook_LTE_ProtocolConfigurationOption.html



This patch is merged with Cedric's patch and tested.

Signed-off-by: Chun-Yeow Yeoh <yeow@tmrnd.com.my>
Signed-off-by: Cedric Roux <Cedric.Roux@eurecom.fr>