Revert "bpf: tcp: Mark bpf_load_hdr_opt() arg2 as read-write"

This reverts commit 670ef7b2 which is
commit 8ac412a3 upstream.

It breaks the Android kernel build and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I0ade325d73909e8d8d61af59d77c6621bbac28db
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>