[IFLIB] When system runs out of mbufs incoming network traffic stops entirely

[Hans Petter Selasky]

Hi,

It appears iflib has a little defect. When the system temporarily runs 
out of mbufs, iflib based network drivers stop receiving packets 
forever, even when the mbuf zone recover.

In mlx5en(4) which doesn't use iflib we have a special watchdog/callout 
to retry filling the RX DMA ring when we are out of mbufs. Can iflib do 
the same?

> [zone: mbuf_cluster] kern.ipc.nmbclusters limit reached

Simply doing "ifconfig down" and "ifconfig up" recovers the adapter:

> igb0: link state changed to DOWN
> igb0: link state changed to UP

--HPS