ice: change q_index variable type to s16 to store -1 value

ice: change q_index variable type to s16 to store -1 value

Fix Flow Director not allowing to re-map traffic to 0th queue when action
is configured to drop (and vice versa).

The current implementation of ethtool callback in the ice driver forbids
change Flow Director action from 0 to -1 and from -1 to 0 with an error,
e.g:

 # ethtool -U eth2 flow-type tcp4 src-ip 1.1.1.1 loc 1 action 0
 # ethtool -U eth2 flow-type tcp4 src-ip 1.1.1.1 loc 1 action -1
 rmgr: Cannot insert RX class rule: Invalid argument

We set the value of `u16 q_index = 0` at the beginning of the function
ice_set_fdir_input_set(). In case of "drop traffic" action (which is
equal to -1 in ethtool) we store the 0 value. Later, when want to change
traffic rule to redirect to queue with index 0 it returns an error
caused by duplicate found.

Fix this behaviour by change of the type of field `q_index` from u16 to s16
in `struct ice_fdir_fltr`. This allows to store -1 in the field in case
of "drop traffic" action. What is more, change the variable type in the
function ice_set_fdir_input_set() and assign at the beginning the new
`#define ICE_FDIR_NO_QUEUE_IDX` which is -1. Later, if the action is set
to another value (point specific queue index) the variable value is
overwritten in the function.

Fixes: cac2a27cd9ab ("ice: Support IPv4 Flow Director filters")
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>