apm821xx: set mib-poll-interval on emac0 attached ar83xx switch
Commit "generic: ar8216: add mib_poll_interval switch attribute" sets
mib-poll-interval as disabled by default (was set to 2s), so it makes
switch LEDs trigger disfunctional on devices which don't have
mib-poll-interval set.
So this patch sets mib-poll-interval to 500ms on devices which have
ar83xx switch connected to emac0, as the same value was set for built in
switches in
443fc9ac35 ("ath79: use ar8216 for builtin switch").
Signed-off-by: Petr Štetiar <ynezz@true.cz>