Changes

gsm0808: fix wrong codec defaults for OFR_AMR_WB
3GPP TS 48.008 chapter 3.2.2.103 states that the configuration bits of 
OFR_AMR_WB are coded as follows:
"S0, S2, S4 indicates the supported Codec Configurations. S1, S3, S5,
S6, S7 are reserved and coded with zeroes."
The current default setting of 0x3F violates this requirement. Lets set 
the "forbidden" settings zu zero and keep only the allowed ones.
Change-Id: I4a481def59e9c98cfdcafc2b80c0ac7df0c14130

gsm0808: add function to convert amr gsm0408 setings to gsm0808
Add a function to convert struct gsm48_multi_rate_conf, which holds the 
codec settings for AMR, to S0-S15 bit representation as defined in 3GPP
TS 48.008 3.2.2.49
Change-Id: I4e656731b16621736c7a2f4e64d9ce63b1064e98 Related: OS#3548