xfrm: Fix replay notification for esn.

We may miscalculate the sequence number difference from the
last time we send a notification if a sequence number wrap
occured in the meantime. We fix this by adding a separate
replay notify function for esn. Here we take the high bits
of the sequence number into account to calculate the
difference.

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