use netmap_rx_irq() and netmap_tx_irq() instead of replicating the
logic in the individual driver.
Fix the man page installation broken in r250079. Pointy hat to me.

Thanks to Florian Smeets for pointing this out and providing a patch.

Submitted by:	Florian Smeets <flo@smeets.im>
Approved by:	jimharris (mentor)