Do a lockless read of the BPF interface structure descriptor list head before grabbing BPF locks to see if there are any entries in order to avoid the cost of locking if there aren't any.  Avoids a mutex lock/ unlock for each packet received if there are no BPF listeners.
Do a lockless read of the BPF interface structure descriptor list head
before grabbing BPF locks to see if there are any entries in order to
avoid the cost of locking if there aren't any.  Avoids a mutex lock/
unlock for each packet received if there are no BPF listeners.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase