UDPLite requires a checksum. Therefore, discard a received packet if
the checksum is 0.

MFC after: 3 days
Make size of Tx and Rx rings configurable

Required size of event queue is calculated now.

Submitted by:   Andrew Rybchenko <arybchenko at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.
Update SolarFlare driver manual page with new tunables.

Submitted by:   Andrew Rybchenko <arybchenko at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.