net: ethernet: dwmac-sun8i: show message only when switching to promisc

Printing the info message every time more than the max number of mac
addresses are requested generates unnecessary log spam.  Showing it only
when the hw is not already in promiscous mode is equally informative
without being annoying.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: David S. Miller <davem@davemloft.net>