sky2: Avoid down and up during sky2_reset

Hi Stephen,

This patch set reimplements sky2_reset so that

* interrupts are disabled during reset
* memory is not free'd and reallocated
* tx queues are stopped during reset, but the device is not brought down

Additionally, it avoids partial initialization of the hardware when ring buffer allocation fails.

The rx ring still needs to be fully allocated for sky2_up to succeed.

thanks,

Mike