realtek: rtl930x: Fetch link status for all ports in switch IRQ

realtek: rtl930x: Fetch link status for all ports in switch IRQ

Link status needs to be read twice, and a single register value is
enough for determining link status for all the ports

It is not necessary to go through each potential port separately and later
actually identify for which ports the interrupt actually was. The helper
for_each_set_bit() directly iterate through all set bits.

While at it, rename the function to a proper naming scheme.

Signed-off-by: Harshal Gohel <hg@simonwunderlich.de>
Co-developed-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Sharadanand Karanjkar <sk@simonwunderlich.de>
Link: https://github.com/openwrt/openwrt/pull/19578
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>