PCUIF: fix coding of 'lqual_cb' field in PCUIF_data

This patch fixes BTS_Tests.TC_pcu_data_ind_lqual_cb, which is currently
failing due to incorrect decoding of the 'lqual_cb' field:

  "Link quality -32512 does not match expected value -256"

The COMP attribute is documented in TITAN's reference guide,
see 4-ttcn3_language_extensions.adoc#attributes for more info.

Change-Id: I79b8cd41010f212898fbf39c4c600ace69603e79
Related: OS#5954
1 file changed