netstat: fix nhop prepend printing.

If present, print nexthop L2 prepend data in hex.

Approved by: re(gjb)
MFC after: 1 week

(cherry picked from commit 731bfa9f180388e4081b64afb94c357643600238)
(cherry picked from commit bea3efc01cb716e8e77d61af085795eb2d0c013c)