net/mlx4_en: Call register_netdevice in the proper location

Netdevice registration should be performed a the end of the driver
initialization flow. If we don't do that, after calling register_netdevice,
device callbacks may be issued by higher layers of the stack before
final configuration of the device is done.

For example (VXLAN configuration race), mlx4_SET_PORT_VXLAN was issued
after the register_netdev command. System network scripts may configure
the interface (UP) right after the registration, which also attach
unicast VXLAN steering rule, before mlx4_SET_PORT_VXLAN was called,
causing the firmware to fail the rule attachment.

Fixes: 837052d0 ("net/mlx4_en: Add netdev support for TCP/IP offloads of vxlan tunneling")
Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>