nfp: sync ring state during FW reconfiguration

FW reconfiguration in .ndo_open()/.ndo_stop() should reset/
restore queue state.  Since we need IRQs to be disabled when
filling rings on RX path we have to move disable_irq() from
.ndo_open() all the way up to IRQ allocation.

nfp_net_start_vec() becomes trivial now so it's inlined.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>