[XFRM]: Compilation warnings in xfrm_user.c.

When CONFIG_SECURITY_NETWORK_XFRM is undefined the following warnings appears:
net/xfrm/xfrm_user.c: In function 'xfrm_add_pol_expire':
net/xfrm/xfrm_user.c:1576: warning: 'ctx' may be used uninitialized in this function
net/xfrm/xfrm_user.c: In function 'xfrm_get_policy':
net/xfrm/xfrm_user.c:1340: warning: 'ctx' may be used uninitialized in this function
(security_xfrm_policy_alloc is noop for the case).

It seems that they are result of the commit
03e1ad7b ("LSM: Make the Labeled IPsec
hooks more stack friendly")

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>