Process the internal call codec update the same as for external call

Sometimes the bridged_chan is not yet available during the
chan_voicemngr_modify_codec() and for internal call there is a
possibility that one side  is setting configured codec (g722 for
example) while other side which does not have yet bridged_chan available
use alaw. To prevent this codec mismatch, do not set alaw codec for
internal as the configured codec is always available for both sides.