myri10ge: improve parity error detection and recovery

Improve myri10ge parity error detection and recovery:
1) Don't restore PCI config space to a rebooted NIC until AFTER the
   host is quiescent.
2) Let myri10ge_close() know the NIC is dead, so it won't waste time
   waiting for a dead nic to respond to MXGEFW_CMD_ETHERNET_DOWN
3) When the NIC is quiet (link down, or otherwise idle link) use
   a pci config space read to detect a rebooted NIC.  Otherwise
   we might never notice that a NIC rebooted

Signed-off-by: Andrew Gallatin <gallatin@myri.com>
Signed-off-by: Brice Goglin <brice@myri.com>
Signed-off-by: David S. Miller <davem@davemloft.net>