[API Frames] Added a method to get the checksum of a packet.
[API Frames] Added a method to get the checksum of a packet.

Signed-off-by: Tatiana Leon <8c4753e861fecbb16ba9ebac0b105a2d4612071d@digi.com>
digidotcom/XBeeJavaLibrary,brucetsao/XBeeJavaLibrary,GUBotDev/XBeeJavaLibrary