r8169: add rtl_disable_rxdvgate()

rtl_disable_rxdvgate() is used for disable RXDV_GATE. It is opposite function
of rtl_enable_rxdvgate().

Disable RXDV_GATE does not have to delay. So in this patch, also remove the
delay after disale RXDV_GATE.

Signed-off-by: Chunhao Lin <hau@realtek.com>
Link: https://lore.kernel.org/r/20220928171356.3951-1-hau@realtek.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>