net: sfp: swap order of rtnl and st_mutex locks

Swap the order of the rtnl and st_mutex locks - st_mutex is now nested
beneath rtnl lock instead of rtnl being beneath st_mutex. This will
allow us to hold st_mutex only while manipulating the module's hardware
or software control state.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>