r8169: keep firmware in memory.

The firmware agent is not available during resume. Loading the firmware
during open() (see eee3a96c) is not
enough.

close() is run during resume through rtl8169_reset_task(), whence the
mildly natural release of firmware in the driver removal method instead.

It will help with http://bugs.debian.org/609538

. It will not avoid
the 60 seconds delay when:
- there is no firmware
- the driver is loaded and the device is not up before a suspend/resume

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Tested-by: Jarek Kamiński <jarek@vilo.eu.org>
Cc: Hayes <hayeswang@realtek.com>
Cc: Ben Hutchings <benh@debian.org>
Signed-off-by: David S. Miller <davem@davemloft.net>