kernel-pfkey: Fix replay window size on FreeBSD and Mac OS X

The FreeBSD and Mac OS X kernels interpret sadb_sa_replay as the size of the
replay window in bytes.  Linux on the other hand does the same for PF_KEY it
does for XFRM so sadb_sa_replay denotes the number of packets/bits in the
window.  Similarly, the window size on Linux is limited to 32 by the four
byte default bitmap used for IPsec SAs (may only be changed with
XFRMA_REPLAY_ESN_VAL), which is not the case on the other platforms.