Packet validation

[KD0NKS]

Per http://www.aprs-is.net/Connecting.aspx

All "packets" sent to APRS-IS must be in the TNC2 format terminated by a carriage return, line feed sequence. No line may exceed 512 bytes including the CR/LF sequence. Only verified (valid passcode) clients may send data to APRS-IS. See the IGate document regarding gating packets to APRS-IS. Packets originating from the client should only have TCPIP in the path, nothing more or less (AE5PL-TS>APRS,TCPIP:my packet). For compatibility, the following rules are for any station generating packets:

• q constructs should never appear on RF. Only the qAR and qAO constructs may be generated by a client (IGate) on APRS-IS.
• The I construct should never appear on RF. This is an out-dated IGate construct which should no longer be used.
• Except for within 3rd party format gated packets, TCPIP and TCPXX should not be used on RF.

[KD0NKS]

512 byte limit has now been implemented in pull request #237.