Reduce overhead of IPSEC for traffic generated from host

When IPSEC is enabled on the kernel the forwarding path has an optimization to not enter the code paths
for checking security policies but first checks if there is any security policy active at all.

The patch introduces the same optimization but for traffic generated from the host itself.
This reduces the overhead by 50% on my tests for generated host traffic without and SP active.

Differential Revision: https://reviews.freebsd.org/D2980
Reviewed by: ae, gnn
Approved by: gnn(mentor)