BSC LCLS: explicitly check for RSL_IE_CHAN_NR

Check that channel number IE is present in the received message. This
fixes following warning:

The value returned by function `@RSL_Types.f_rsl_find_ie' is not used

Change-Id: Icc6824d7acef809d76c70b5ff060a8261a82e2be
Related: OS#3659
1 file changed