infiniband: make sure the src net is infiniband when create new link

infiniband: make sure the src net is infiniband when create new link

When we create a new infiniband link with uninfiniband device, e.g. `ip link
add link em1 type ipoib pkey 0x8001`. We will get a NULL pointer dereference
cause other dev like Ethernet don't have struct ib_device.

The code path is:
rtnl_newlink
  |-- ipoib_new_child_link
        |-- __ipoib_vlan_add
              |-- ipoib_set_dev_features
                    |-- ib_query_device

Fix this bug by make sure the src net is infiniband when create new link.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>