bnx2x: Configurable pause scheme

When a given ring is running out of space, the FW can send pause towards the
network. When working with multi-queues, when one queue is getting out of space
it can block all other queues. The preferred scheme is to send pause frames only
when running out of the shared internal chip buffers and if a given queue cannot
place a packet on the host, it will drop it. Since some users might want to work
in drop-less mode, allowing changing the behavior as a module parameter.

Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>