ENDC S1-U gNB support: Separate some GTP functions between eNB and gNB. Downlink traffic from SGW arrives properly at gNB now after path switch

Mainly comestics and integer type management

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

	ACKNOWLEDGEMENT:
 	1. This commit was developed at Vicomtech (https://www.vicomtech.org) under UE project CDN-X-ALL: "CDN edge-cloud computing for efficient cache and reliable streaming aCROSS Aggregated unicast-multicast LinkS"
 	2. Project funded by Fed4FIRE+ OC5 (https://www.fed4fire.eu

)

Signed-off-by: javier.morgade@ieee.org <javier.morgade@ieee.org>

Using the basic simulator and valgrind, it was found that
the lack of initialization of those two pointers leads to
some very nasty behavior of some other parts of the system.