Merge branch 'stmmac-Enable-Flow-Control'

Jose Abreu says:

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net: stmmac: Enable Flow Control

I don't know of any specific reason why Flow Control is off by default but
do let me know if there is any.

Tested in B2B between XGMAC2 and GMAC5.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>