Support pseudo mpls interface from netspoc.

- Read unnumbered interface for NX-OS.
- Read 'mpls ip' for IOS and NX-OS.
Ignore multiple mpls interfaces named 'mpls.*'
Add support for dns, unidirectional in twice NAT.
v1.082

 - Added support for attributes 'dns' and 'unidirectional' in twice NAT.
 - Unnumbered interface with name 'mpls' from Netspoc is silently ignored,
   if device has some interface with 'ip mpls'.