Revert "bpf, sockmap: Handle fin correctly"

This reverts commit 3a2129eb.

It breaks the Android KABI and will be brought back at a later time when
it is safe to do so.

Bug: 161946584
Change-Id: Ib4d8c98270484b4d2c63e838bbe0d24c00642f87
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>