bpf: x86: add missing 'shift by register' instructions to x64 eBPF JIT

'shift by register' operations are supported by eBPF interpreter, but were
accidently left out of x64 JIT compiler. Fix it and add a testcase.

Reported-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Fixes: 62258278 ("net: filter: x86: internal BPF JIT")
Signed-off-by: David S. Miller <davem@davemloft.net>