BUG 6487: Extra routes to IVpnLink endpoint not in FIB

BUG 6487: Extra routes to IVpnLink endpoint not in FIB

 + LportTag range for InterVpnLink endpoints has changed to a range of
   [170001..270000]. Those values does not fit in a uint16 attribute

 + Also applies a bit of refactoring to reduce the duplication of code
   as much as possible

 + It also aligns the system properties names to the ones defined
   in sdnc repository

 Apart from above bug fix this commit also deals with:

 1> Fixes in metadata writing
 2> InterVpnLink Active even if VPN not exists

Change-Id: Iafe72a651153a7ca48e68748c6b7b271541e835c
Signed-off-by: Suraj Ranjan <suraj.ranjan@ericsson.com>