Revert "ipv4, ipv6: Use splice_eof() to flush"

This reverts commit 2489502f which is
commit 1d7e4538 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: I3c68663b0b8f6295ae1f8b119dfa243579e1cdd6
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>