Ts28.541 rel16 cr0489 correct the description for gnbdu function and ep ng c
requested to merge TS28.541_Rel16_CR0489_Correct_the_description_for_GNBDUFunction_and_EP_NgC into Integration_Rel16_SA5_137_YANG
Correct the description for GNBDUFunction and EP_NgC Rel-16 28.541 CR 489 S5-213157 merged to integration by Balazs after SA5#137