stream_out: dlna: replace sprintf by iostream
The DLNA info must match with:
- DNLA.ORG_OP is 2 character-wide 0-padded
- DNLA.ORG_FLAGS is 32 character-wide 0-padded.
Use std::setfill and then set the appropriate width for each fields in the info, directly into the DLNA istringstream used to serialize the whole string.