flac packetizer: cosmetics

C99, brace style, space
No functional changes
flac packetizer: move functions

remove prototypes
flac packetizer: simplify header parsing
flac packetizer: avoid realloc
flac packetizer: Use meaningful names for block_t
flac packetizer: verbose error message
flac packetizer: small factorization when first PTS has not arrived
flac packetizer: deindent switch
flac packetizer: validate frames with their CRC

Fix #9442