Rework reference counting in case we queue into the netisr, or overflow the netisr queue and fall back to the interface queue so that we can garuantee that the ifnet pointer stays valid.   Formerly we ended up with reference counts <= 0 in case the netisr had returned ENOBUFS.  The idea is to track any packet in the netisr queue and only change the refount on edge operations for the fallback interface queue. This also avoids problems in case the if_snd.ifq_len lies to us.
Rework reference counting in case we queue into the netisr,
or overflow the netisr queue and fall back to the interface
queue so that we can garuantee that the ifnet pointer stays
valid.   Formerly we ended up with reference counts <= 0 in
case the netisr had returned ENOBUFS.  The idea is to track
any packet in the netisr queue and only change the refount
on edge operations for the fallback interface queue. This
also avoids problems in case the if_snd.ifq_len lies to us.

Also rework refount assertions to make sure they trigger if
we go below 1. Formerly a negative refence count did not
trigger the assert as the refcount variable is u_int.

Sponsored by:	ISPsystem
MFC after:	5 days

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