net: mvpp2: Add TX flow control support for jumbo frames

With MTU less than 1500B on all ports, the driver uses per CPU pool mode.
If one of the ports set to jumbo frame MTU size, all ports move
to shared pools mode.
Here, buffer manager TX Flow Control reconfigured on all ports.

Signed-off-by: Stefan Chulski <stefanc@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>