Revert "ipv4: ip_tunnel: Unmask upper DSCP bits in ip_tunnel_bind_dev()"

This reverts commit 5fb41d9b which is
commit e7191e51 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I2eb3e1b378561ab75ccb03904452e37e2385bfa2
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>