[IPSEC]: Move type and mode map into xfrm_state.c

[IPSEC]: Move type and mode map into xfrm_state.c

The type and mode maps are only used by SAs, not policies.  So it makes
sense to move them from xfrm_policy.c into xfrm_state.c.  This also allows
us to mark xfrm_get_type/xfrm_put_type/xfrm_get_mode/xfrm_put_mode as
static.

The only other change I've made in the move is to get rid of the casts
on the request_module call for types.  They're unnecessary because C
will promote them to ints anyway.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>