[XFRM]: Move xfrm_nl to xfrm_state.c from xfrm_user.c

xfrm_user could be modular, and since generic code uses this symbol
now...

Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/xfrm/xfrm_state.c
Simple merge

diff --cc net/xfrm/xfrm_user.c
Simple merge