UMTS_FP: fix handling reserved C/T value

The spec puts the reserved value at 0xf but our internal table has 'unknown' at
0; since all the other values seem to be offset-by-one, just take the modulus
0xf to avoid running off the end of the table.

Bug: 12191
Change-Id: I83c8fb66797bbdee52a2246fb1eea6e37cbc7eb0
Reviewed-on: https://code.wireshark.org/review/15722
Reviewed-by: Evan Huus <eapache@gmail.com>
Petri-Dish: Evan Huus <eapache@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>
dissect_common_timing_advance(packet_info *pinfo, proto_tree *tree, tvbuff_t *tvb, int offset)
{
    guint8  cfn;
    guint16 timing_advance;

    /* CFN control */
    cfn = tvb_get_guint8(tvb, offset);
    proto_tree_add_item(tree, hf_fp_cfn_control, tvb, offset, 1, ENC_BIG_ENDIAN);
    offset++;

    /* Timing Advance */
    timing_advance = (tvb_get_guint8(tvb, offset) & 0x3f) * 4;
    proto_tree_add_uint(tree, hf_fp_timing_advance, tvb, offset, 1, timing_advance);
    offset++;

    col_append_fstr(pinfo->cinfo, COL_INFO, " CFN = %u, TA = %u",
                    cfn, timing_advance);

    return offset;
}

dissect_common_timing_advance(packet_info *pinfo, proto_tree *tree, tvbuff_t *tvb, int offset)
{
    guint8  cfn;
    guint16 timing_advance;

    /* CFN control */
    cfn = tvb_get_guint8(tvb, offset);
    proto_tree_add_item(tree, hf_fp_cfn_control, tvb, offset, 1, ENC_BIG_ENDIAN);
    offset++;

    /* Timing Advance */
    timing_advance = (tvb_get_guint8(tvb, offset) & 0x3f) * 4;
    proto_tree_add_uint(tree, hf_fp_timing_advance, tvb, offset, 1, timing_advance);
    offset++;

    col_append_fstr(pinfo->cinfo, COL_INFO, " CFN = %u, TA = %u",
                    cfn, timing_advance);

    return offset;
}
