Apply port RX/TX enable operations only to active switch ports.

RapidIO specification (Part 6: LP-Serial Physical Layer) recommends to
keep Output Port Enable (TX) and Input Port Enable (RX) control bits in
disabled state (0b0) after device reset.  It also allows to have
implementation specific reset state for these bits.

This patch ensures that TX/RX enable action is applied only to active
switch's ports while preserving an initial state of inactive ones.

This patch is intended to keep inactive switch ports with inbound and
outbound packet transfers disabled to block unexpected packets during hot
insertion event.  While it does not fix any visible malfunction it is
intended to prevent such events in future.
Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>