net/sfc/base: reduce filter priorities to implemented only

net/sfc/base: reduce filter priorities to implemented only

Only implemented filter priorities are manual and auto. Remove
unused priorities since exposing unimplemented functionality
is of no benefit.

Tx filter specification default priority is changed to manual,
since required priority does not differ from it in the implementation.

Fixes: f9565517ff4f ("net/sfc/base: import filters support")
Cc: stable@dpdk.org
Signed-off-by: Igor Romanov <igor.romanov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>