net/mlx4_en: Do not allocate redundant TX queues when TC is disabled

Currently the number of TX queues that are allocated doesn't depend
on the number of TCs, the module always loads with max num of UP
per channel.
In order to prevent the allocation of unnecessary memory, the
module will load with minimum number of UPs per channel, and the
user will be able to control the number of TX queues per channel
by changing the number of TC to 8 using the tc command.
The variable num_up will hold the information about the current
number of UPs.
Due to the change, needed to remove the lines that set the value of
UP to be different than zero in the func "mlx4_en_select_queue",
since now the num of TX queues that are allocated is only one per channel
in default.
In order not to force the UP to be zero in case of only one TC, added
a condition before forcing it in the func "mlx4_en_fill_qp_context".

Tested:
After the module is loaded with minimum number of UP per channel, to
increase num of TCs to 8, use:
tc qdisc add dev ens8 root mqprio num_tc 8
In order to decrease the number of TCs to minimum number of UP per channel,
use:
tc qdisc del dev ens8 root

Signed-off-by: Inbar Karmy <inbark@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Cc: Tarick Bedeir <tarick@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>