MFC 290028:
Turning on IPSEC used to introduce a slight amount of performance
degradation (7%) for host host TCP connections over 10Gbps links,
even when there were no secuirty policies in place. There is no
change in performance on 1Gbps network links. Testing GENERIC vs.
GENERIC-NOIPSEC vs. GENERIC with this change shows that the new
code removes any overhead introduced by having IPSEC always in the
kernel.

Differential Revision: D3993
Sponsored by: Rubicon Communications (Netgate)