VPN SAFI support

Next Hop needs to be specified in each extension:

http://tools.ietf.org/html/rfc4760:

Network Address of Next Hop:

A variable-length field that contains the Network Address of
the next router on the path to the destination system. The
Network Layer protocol associated with the Network Address of
the Next Hop is identified by a combination of <AFI, SAFI>
carried in the attribute.

http://tools.ietf.org/html/draft-ietf-idr-ls-distribution-04#section-3.4

• therefore we cannot put NextHop information into Attributes-NextHop. Carry it always in MP_REACH.