NMap scans extremely slow on FreeBSD 10, possibly BIOCIMMEDIATE

[Ken Harvey]

I am attempting to troubleshoot a problem with nmap on FreeBSD 10.
The issue that I am having is that when running nmap -O 10.1.2.3 it is
taking around 220 seconds to complete.  While if I run that same
command using Windows or Linux the command completes in around 2.3
seconds.
Currently FreeBSD is 100 times slower for nmap scans then Linux or Windows.

After reading through the forums and the mailing list archives I think
the problem may be associated with BIOCIMMEDIATE.  bpf is waiting for
the buffer to fill, or for the ttl to expire before it processes the
packets, rather than processing them upon receiving them.  I may be
incorrect in this theory, but I am unsure how to verify plausibility.
While looking at /usr/includes/net/bpf.h I do see that BIOCIMMEDIATE
is implemented.  So I am now wondering if nmap or libpcap is sending
the proper switch to bpf for it to enable BIOCIMMEDIATE.
Is there a way for me to verify whether BIOCIMMEDIATE is being called in bpf?
Is there a better way for me to try and troubleshoot this issue?

You can view my forum post at
https://forums.freebsd.org/viewtopic.php?f=7&t=45286
It has a little bit more detail then this post, but it also has a lot
of my random troubleshooting steps as well.

Currently I am a little over my head, and I am unsure how to or where
to begin troubleshooting this problem.
While I do want to get this issue resolved, I also would like to learn
how to troubleshoot issues like these.

Any help or guidance would be greatly appreciated.