tsnep: Add functions for queue enable/disable

Move queue enable and disable code to separate functions. This way the
activation and deactivation of the queues are defined actions, which can
be used in future execution paths.

This functions will be used for the queue reconfiguration at runtime,
which is necessary for XSK zero-copy support.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>