r8169: do not bring device down when suspending

Stopping all activity through ChipCmd and blindly acking the irqs
is neither nice nor completely needed: the transition to low-power
mode does enough work and it apparently keeps the device in a sane
state.

Patch suggested by a fix for http://bugzilla.kernel.org/show_bug.cgi?id=9512



The rtl_shutdown path is kept unchanged so far.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Tested-by: Anders Eriksson <aeriksson@fastmail.fm>
Cc: Edward Hsu <edward_hsu@realtek.com.tw>
Signed-off-by: David S. Miller <davem@davemloft.net>