ipaddress: Make sure VF min/max rate API is supported before using it

ipaddress: Make sure VF min/max rate API is supported before using it

When using the new minimum rate API and providing only one parameter
(minimum rate/maximum rate), we query the VF min and max rate regardless
of kernel support.
This resulted in segmentation fault in ipaddr_loop_each_vf, which tries
to access NULL pointer.

This patch identifies such cases by testing the VF table for NULL
pointer in IFLA_VF_RATE, and aborts the operation.
Aborting on the first VF is valid since if the kernel does not support
the new API for the first VF, it will not support it for the other VFs
as well.

Fixes: f89a2a05ffa9 ("Add support to configure SR-IOV VF minimum and maximum Tx rate through ip tool")
Cc: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
Signed-off-by: Gal Pressman <galp@mellanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>