Update gorouter submodule

Follow up to PR:
- #331
- cloudfoundry/gorouter#356

In 0c84493, the gorouter submodule points to a commit within the branch.
Our CI cannot automatically update from that floating commit:
```
Cloning into '/tmp/build/get/src/code.cloudfoundry.org/gorouter'...
fatal: reference is not a tree: 1aad53f46205caa06e11cdd04885e9dd7fa7cd45
fatal: Unable to checkout '1aad53f46205caa06e11cdd04885e9dd7fa7cd45' in submodule path 'src/code.cloudfoundry.org/gorouter'
```
CI Build: https://ci.funtime.lol/teams/networking/pipelines/routing/jobs/bump-dependencies-go-mod/builds/22

This commit changes the submodule reference back to to origin/main so we
can actually consume our updates.

Author: jrussett