seccomp: use a default value of 0 for the mask
seccomp: use a default value of 0 for the mask

The mask was unconditionally parsed, it failed if no mask was
provided.

Signed-off-by: Felix Abecassis <55aebb135999a2c3fc3e3a88716154833ef9e5ed@nvidia.com>

caglar10ur/lxc,hallyn/lxc,caglar10ur/lxc,hallyn/lxc,ss1h2a3tw/lxc,caglar10ur/lxc,ss1h2a3tw/lxc,hallyn/lxc,ss1h2a3tw/lxc