net: mscc: ocelot: rename aggr_count to num_ports_in_lag

It makes it a bit easier to read and understand the code that deals with
balancing the 16 aggregation codes among the ports in a certain LAG.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit 21357b61)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
[Xulin: Original patch taken from
https://github.com/vladimiroltean/linux/commits/felix-dsa-tag-vlan-stable

]
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>