[NET]: should explicitely initialize atomic_t field in struct dst_ops

All but one struct dst_ops static initializations miss explicit
initialization of entries field.

As this field is atomic_t, we should use ATOMIC_INIT(0), and not
rely on atomic_t implementation.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>