Revert "net: release reference to inet6_dev pointer"

This reverts commit 5e13e69d which is
commit 5cb24968 upstream.

It breaks the Android ABI, and is already merged in the non-LTS branch
in an abi-safe way.

Bug: 161946584
Change-Id: I563f7eb7ffb01d9681f6a1dbb0252ca32b94f856
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>