Revert "xfrm: policy: Read seqcount outside of rcu-read side in xfrm_policy_lookup_bytype"

This reverts commit d7b04089.

This commit tried to fix a locking bug introduced by commit 77cc278f
("xfrm: policy: Use sequence counters with associated lock"). As it
turned out, this patch did not really fix the bug. A proper fix
for this bug is applied on top of this revert.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>