RFC - Support in VDP22 for correct error code/status to vdptool

This commit has the following changes:
a. Returning the status or error code to vdptool for the error cases. Errors
can be Tx error, invalid parameters, incorrect configuration etc. The vdptool
 is modified to print the error messages from lldpad.
b. Modify the vdptool option from set-tlv/get-tlv to set-vsi/get-vsi. The
 vdptool man page document is also modified accordingly.
c. Re-arrange the definitions in header files.
d. Fix some formatting issues.

Signed-off-by: padkrish <padkrish@cisco.com>
Signed-off-by: None <None>