net: dsa: felix: actually disable flooding towards NPI port

The two blamed commits were written/tested individually but not
together.

When put together, commit 90897569 ("net: dsa: felix: start off with
flooding disabled on the CPU port"), which deletes a reinitialization of
PGID_UC/PGID_MC/PGID_BC, is no longer sufficient to ensure that these
port masks don't contain the CPU port module.

This is because commit b903a6bd ("net: dsa: felix: migrate flood
settings from NPI to tag_8021q CPU port") overwrites the hardware
default settings towards the CPU port module with the settings that used
to be present on the NPI port treated as a regular port. There, flooding
is enabled, so flooding would get enabled on the CPU port module too.

Adding conditional logic somewhere within felix_setup_tag_npi() to
configure either the default no-flood policy or the flood policy
inherited from the tag_8021q CPU port from a previous call to
dsa_port_manage_cpu_flood() is getting complicated. So just let the
migration logic do its thing during initial setup (which will
temporarily turn on flooding), then turn flooding off for the NPI port
after felix_set_tag_protocol() finishes. Here we are in felix_setup(),
so the DSA slave interfaces are not yet created, and this doesn't affect
traffic in any way.

Fixes: 90897569 ("net: dsa: felix: start off with flooding disabled on the CPU port")
Fixes: b903a6bd ("net: dsa: felix: migrate flood settings from NPI to tag_8021q CPU port")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>