Get 82574 tx queues working reliably via a few bits of stolen errata and
a few bits of stolen igb(4) code.

• Bind interrupts to specific CPUs (stolen from igb).
• Don't ever let em_mq_start() have a negative value for its tx queue.
• Allow the interrupt for the link status to be shareable.
• Setup 2nd queue TXDCTL bits to enable it fully, without this, it times out. Values derived from linux e1000e driver, netdev.c. Committed due to apparent erratum.
• When configuring RSS, use a modulo of the num_rx_queues, instead of magic number 2
• Add premptive comment when configuring RXDCTL indicating why the 2nd queue is not being configured here.
• Revert enhanced queue status handling, from svn revision 281045 as it fails to handle watchdog events at all in this driver.