MIPS: BPF: Use unsigned access for unsigned SKB fields.

The SKB vlan_tci and queue_mapping fields are unsigned, don't sign
extend these in the BPF JIT.  In the vlan_tci case, the value gets
masked so the change is not needed for correctness, but do it anyway
for agreement with the types defined in struct sk_buff.

Signed-off-by: David Daney <david.daney@cavium.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Steven J. Hill <steven.hill@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15746/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>