selftests/bpf: Skip all serial_test_get_branch_snapshot in vm

selftests/bpf: Skip all serial_test_get_branch_snapshot in vm

Skipping the second half of the test is not enough to silent the warning
in dmesg. Skip the whole test before we can either properly silent the
warning in kernel, or fix LBR snapshot for VM.

Fixes: 47b7406a68ed ("selftests/bpf: Add test for bpf_get_branch_snapshot")
Fixes: a9d5ec5f52d1 ("selftests/bpf: Skip the second half of get_branch_snapshot in vm")
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211026000733.477714-1-songliubraving@fb.com