net/enic: fix Rx queue init after restarting a device

net/enic: fix Rx queue init after restarting a device

If you stop, then start a port that had already received some packets,
the NIC could fetch discriptors from the wrong location. This could
effectivly reduce the size of the Rx queue by a random amount and
cause packet drop or reduced performance.

Reset the NIC fetch index to 0 when allocating and posting mbuf
addresses to the NIC.

Fixes: 947d860c821f ("enic: improve Rx performance")

Signed-off-by: John Daley <johndale@cisco.com>
Reviewed-by: Nelson Escobar <neescoba@cisco.com>