Revert "bpf: program: Refuse non-O_RDWR flags in BPF_OBJ_GET"

This reverts commit d37300ed.

Looks like it breaks vts-core/gce/vts-presubmit-kernel-kernel-triggered
on kernel_virt_x86_64 on aosp_kernel-common-android-mainline

Will do more digging later, revert it for now.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ide1562bce106d02f4058874f5696fa0662a85731