mlxsw: spectrum_trap: Factor out common Rx listener function

We currently have an Rx listener function for exception traps that marks
received skbs with 'offload_fwd_mark' and injects them to the kernel's
Rx path. The marking is done because all these exceptions occur during
L3 forwarding, after the packets were potentially flooded at L2.

A subsequent patch will add support for control traps. Packets received
via some of these control traps need different handling:

1. Packets might not need to be marked with 'offload_fwd_mark'. For
   example, if packet was trapped before L2 forwarding

2. Packets might not need to be injected to the kernel's Rx path. For
   example, sampled packets are reported to user space via the psample
   module

Factor out a common Rx listener function that only reports trapped
packets to devlink. Call it from mlxsw_sp_rx_no_mark_listener() and
mlxsw_sp_rx_mark_listener() that will inject the packets to the kernel's
Rx path, without and with the marking, respectively.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>