net/dot1ag-utils: dot1ag_ccd memory leaks

Be very aware that dot1ag_ccd may be leaking memory like crazy.

I enabled it last week on a spare re(4) port, and it had a 5GiB RES when 
I scheduled reboot to take my primary metal to 15.1p2 roday

I took a private mirror of what was left on GitHub to SourceHut, of 
course, and that is what the port is built from, but not all head 
revisions from the other forks have been integrated.

It's good enough to provide Layer 2 ping functionality, but I wouldn't 
depend on it as a down MEP responder just yet, and that should be in 
sys/net in base anyway. It's already in Open vSwitch.