Changes

gsm48_ie: add helper function for speech bearer cap on GSM MS side

The speech version list part of TS 24.008 section 10.5.4.5 bearer
capability IE is valid only in the MS->network direction, and will
thus only need to be set by GSM MS implementations.  The "natural"
input to the construction of this IE is the list of supported speech
codecs in the order of preference, but spec-compliant output requires
additional quirks:

* Radio channel requirement bits need to be set based on the v1-only
  subset of the full speech version list;

* There is a curious requirement (commonly ignored by other implementors)
  that the full form of the speech version list shall be elided from
  the final output if only v1 codecs are supported.

Provide a helper function that finishes filling out the full
struct gsm_mncc_bearer_cap after the caller has set only the speech
version list and the CTM support flag.

Change-Id: Iaf41687da1d377e98f26e6a16d991ab7d95be0fc