Revert "arp: Prevent overflow in arp_req_get()."

This reverts commit 97eaa295 which is
commit a7d60277 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: I05947b1018c5e28cdcb891edddf72163a2a0666a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>