Revert "net: inet: Open code inet_hash2 and inet_unhash2"

This reverts commit be1ceb8b which is
commit e8d00590 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: I12120ec99b50bb671a10272766641545051785e0
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>