capabilities: call has_ns_capability from has_capability

Declare the more specific has_ns_capability first in the code and then call it
from has_capability.  The declaration reversal isn't stricty necessary since
they are both declared in header files, but it just makes sense to put more
specific functions first in the code.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>