This is a WAR for DHCP failure after rebooting from the L4T kernel. The
r8169.c kernel driver is setting bit 19 of the rt816x HW register 0xF0,
which goes by FuncEvent and MISC in various driver source/datasheets.
That bit is called RxDv_Gated_En in the r8169.c kernel driver. Clear it
here at the end of probe to ensure that U-Boot can get an IP assigned
via DHCP.
Signed-off-by: NTom Warren <twarren@nvidia.com>