Fix slow frame handling

[sans-ltd]

• During our tests with recorded data from a cars CAN bus (500kBit/s) we had a loss of over 90% while forwarding from CAN0 to CAN1.
• The main reason are were the sleeps in task_CAN()
• To overcome the sleeps without stability issues, we moved the creation of the queues to _init()
• The creation and deletion if the tasks ist still active, as introduced in the fix to assert failed: spinlock_acquire spinlock.h:122 #48
• In addition, the extra init of task_LowLevelRX() was cleaned up