r8169: simplify setting PCI_EXP_DEVCTL_NOSNOOP_EN

r8168b_0_hw_jumbo_enable() and r8168b_0_hw_jumbo_disable() both do the
same and just set PCI_EXP_DEVCTL_NOSNOOP_EN. We can simplify the code
by moving this setting for RTL8168B to rtl_hw_start_8168().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>