net: hns: fix wrong head when modify the tx feature when sending packets

Upon changing the tx feature, the hns driver will modify the
maybe_stop_tx() and fill_desc() functions, if the modify happens
during packet sending, will cause the hardware and software
pointers do not match, and the port can not work anymore.

This patch deletes the maybe_stop_tx() and fill_desc() functions
modification when setting tx feature, and use the skb_is_gro()
to determine which functions to use in the tx path.

Fixes: 38f616da

 ("net:hns: Add support of ethtool TSO set option for Hip06 in HNS")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Jijie Shao <shaojijie@huawei.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>