[SNMP4J] 3DES implementation

[Yue Zhang]

Hi Jochen & Frank,

I'm using SNMP4J 3DES to test a SNMP agent. Found the implementation of 
Priv3DES::extendShortKey() is different from the definition in the Internet 
Draft 'Extension to the User-Based Security Model (USM) to Support Triple-DES 
EDE.

According to the draft section 2.1, the P2K algorithm takes the key as 
Input_bits generated by P2K call in the previous iteration. But 
Priv3DES::extendShortKey() takes the extended-key as input. Could you please 
confirm if it's a bug?

Thanks,
Yue