hsr: fix don't prune the master node from the node_db

Don't prune the master node in the hsr_prune_nodes function.
Neither time_in[HSR_PT_SLAVE_A] nor time_in[HSR_PT_SLAVE_B]
will ever be updated by hsr_register_frame_in for the master port.
Thus, the master node will be repeatedly pruned leading to
repeated packet loss.
This bug never appeared because the hsr_prune_nodes function
was only called once. Since commit 5150b45f
("net: hsr: Fix node prune function for forget time expiry") this issue
is fixed unveiling the issue described above.

Fixes: 5150b45f ("net: hsr: Fix node prune function for forget time expiry")
Signed-off-by: Andreas Oetken <andreas.oetken@siemens.com>
Tested-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>