NCP: cast to guint instead of gulong

Change-Id: Idc8f8f3177703ce5546b8a472034705cb6070707
Reviewed-on: https://code.wireshark.org/review/4666
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
(cherry picked from commit fb27a682a14ca653b36878186e0ddfdc1fea3a4e)
Reviewed-on: https://code.wireshark.org/review/4669