Signed-off-by: vedganes <vedavinayagam.ganesan@nokia.com>

Changes include SAI support for voq neighbor. VOQ neighbor requires an
additional attribute to set the encap index. For local neighbors the
encap index iis assigned by SAI, if not imposed. For remote neighbors,
the encap index is required to be supplised by the upper layer. The
changes validate these conditions for remote neighbors.

Signed-off-by: vedganes <vedavinayagam.ganesan@nokia.com>

Code review comments fix 1

Signed-off-by: vedganes <vedavinayagam.ganesan@nokia.com>

Code review comments fix 2