Lookahead does not work on bmv2

[mihaibudiu]

The following program generates JSON which crashes BMv2:

#include <core.p4>
#include <v1model.p4>

header ethernet_t {
    bit<48> dstAddr;
    bit<48> srcAddr;
    bit<16> etherType;
}

struct M {
}

struct H {}

control DeparserI(packet_out packet, in H hdr) {
    apply {
    }
}

parser parserI(packet_in pkt, out H hdr, inout M meta, inout standard_metadata_t stdmeta) {
    state start {
        transition select(pkt.lookahead<ethernet_t>().etherType)
        {
            0x1000 &&& 0x1000 : accept;
        }
    }
}

control cIngress(inout H hdr, inout M meta, inout standard_metadata_t stdmeta) {
    apply {
    }
}

control cEgress(inout H hdr, inout M meta, inout standard_metadata_t stdmeta) {
    apply {
    }
}
control vc(in H hdr, inout M meta) {
    apply {
    }
}
control uc(inout H hdr, inout M meta) {
    apply {
    }
}

V1Switch(parserI(), vc(), cIngress(), cEgress(), uc(), DeparserI()) main;