net/mlx5e: Switchdev representors are not vlan challenged

Before this patch, mlx5 representors advertised the
NETIF_F_VLAN_CHALLENGED bit, this could lead to missing features when
using reps with vxlan/bridge and maybe other virtual interfaces,
when such interfaces inherit this bit and block vlan usage in their
topology.

Example:
$ip link add dev bridge type bridge
 # add representor interface to the bridge
$ip link set dev pf0hpf master
$ip link add link bridge name vlan10 type vlan id 10 protocol 802.1q
Error: 8021q: VLANs not supported on device.

Reps are perfectly capable of handling vlan traffic, although they don't
implement vlan_{add,kill}_vid ndos, hence, remove
NETIF_F_VLAN_CHALLENGED advertisement.

Fixes: cb67b832 ("net/mlx5e: Introduce SRIOV VF representors")
Reported-by: Roopa Prabhu <roopa@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>