Received frames were passed to the RTL8139 from the network thread,
raising the ASIC interrupt there and racing SIIDRebuild() on the SH-4
thread. Queue them and deliver them from an SH-4 scheduler callback.
Sent frames were pushed into picoTCP from the SH-4 thread, but picoTCP
is built without PICO_SUPPORT_MUTEX so its device queue is unlocked.
Queue them and feed them to picoTCP from the pico thread before each
stack tick.
[ci skip]
Rich Stokes
38a3d83c77