Commit 0017c0b5 "xfrm: Fix replay notification for esn." is off by one
for the sequence number wrapped case as UINT_MAX is 0xffffffff, not
0x100000000. ;)

Just calculate the diff like done everywhere else in the file.
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>