kern/165903: mbuf leak

[Chris Forgeron]

I was already starting to load up a fresh 9.1-STABLE box for other testing, I will also create a stock box (no changes anywhere) and let it idle for a few days to see if the problem is still there. 

I'll report back either way in the next few days with results. 

If I still have problems, I will send the full diags as mentioned below.

Thanks. 

>> 1. This PR does not contain output from "dmesg" nor "pciconf -lvbc", 
>> nor does your Email.  Output from this matters.
>> 
>> 2. Please try 9.1-STABLE and see if there is an improvement; there 
>> have been a huge number of changes/fixes to em(4) between 9.1-RELEASE 
>> and now.  You can try this:
>> 
>> https://pub.allbsd.org/FreeBSD-snapshots/amd64-amd64/9.1-RELENG_9-r249
>> 290-JPSNAP/
>
>Other output that would be useful on a machine where the current mbuf count is actively very high:
>
>* vmstat -z
>* netstat -Q
>* netstat -n -x
>
>It would also be beneficial to provide any sysctl.conf and loader.conf adjustments you do.