rsl: don't send legacy Chan Ident IE for Nokia BTS
The description of CHAN ACTIV command message in TS 48.058 section 8.4.1 lists Channel Identification as an optional IE, with a note that reads "Included if compatibility with phase1 is required." This note may have been misinterpreted as referring to compatibility with Phase 1 phones - but since this network-internal Abis detail is invisible to phones, the real intent of GSM spec authors here must have been compatibility with Phase 1 BTS.
Previous versions of OsmoBSC would always include this IE, and it appears that all previously supported BTS models would simply ignore it. However, newer Nokia BTS models (observed on Flexi Multiradio at least) dislike this IE and return CHAN ACTIV NACK with an optional IE error cause if it is included.
To avoid changing OsmoBSC behavior for other users, let us conditionalize removal of this legacy IE on Nokia BTS for now. This change has been tested on InSite, MetroSite and Flexi Multiradio - no adverse effects on previously supported *Site models.
