otDnsTxtEntry struct

The TXT record key string. If `mKey` is not NULL, then it MUST be a null-terminated C string. The entry is treated as key/value pair with `mValue` buffer providing the value. - The entry is encoded as follows: - A single string length byte followed by "key=value" format (without the quotation marks). - In this case, the overall encoded length must be 255 bytes or less. - If `mValue` is NULL, then key is treated as a boolean attribute and encoded as "key" (with no `=`). - If `mValue` is not NULL but `mValueLength` is zero, then it is treated as empty value and encoded as "key=". If `mKey` is NULL, then `mValue` buffer is treated as an already encoded TXT-DATA and is appended as is in the DNS message.