NCP: switch to wmem memory and ensure that all fields are initialized

Change-Id: Ia17e189baed05d8020654e6702a51f51bd384f26
Reviewed-on: https://code.wireshark.org/review/4589
Reviewed-by: Evan Huus <eapache@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>