protobuf: Convert vma_entry to PB format v3

v2:
 - Use regular uint types in message proto
 - Use PB engine for "show"
v3:
 - drop usage of temp. variable in prepare_shmem_pid

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>