staging: et131x: Fix stats->rx_packets accounting

The net_device_stats->rx_packets counter is not getting updated.
This is due to checking a fMP_ADAPTER_LINK_DETECTION flag prior to
updating which is never set.

Solved by using netif_carrier_ok() to test for a link, and removing
the fMP_ADAPTER_LINK_DETECTION flag, which looks to be a broken
mechanism.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>