net: wwan: Fix MRU mismatch issue which may lead to data connection lost

In pci_generic.c there is a 'mru_default' in struct mhi_pci_dev_info.
This value shall be used for whole mhi if it's given a value for a specific product.
But in function mhi_net_rx_refill_work(), it's still using hard code value MHI_DEFAULT_MRU.
'mru_default' shall have higher priority than MHI_DEFAULT_MRU.
And after checking, this change could help fix a data connection lost issue.

Fixes: 5c2c8531

 ("bus: mhi: pci-generic: configurable network interface MRU")
Signed-off-by: Shujun Wang <wsj20369@163.com>
Signed-off-by: Slark Xiao <slark_xiao@163.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>