xfrm: replay: remove last replay indirection

This replaces the overflow indirection with the new xfrm_replay_overflow
helper.  After this, the 'repl' pointer in xfrm_state is no longer
needed and can be removed as well.

xfrm_replay_overflow() is added in two incarnations, one is used
when the kernel is compiled with xfrm hardware offload support enabled,
the other when its disabled.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>