Update the route package to git rev 6b27048a.

Introduce the following changes:
 - 6b27048 route: drop support for go1.5
 - b7fd658 route: fix typo
 - 41bba8d route: add support for the manipulation of routing informaion

Updates #19967

Change-Id: Id2bb93df97a45254a2df2b048db0143e3e52bbdf
Reviewed-on: https://go-review.googlesource.com/40830
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>