ConnectivityManager: fix documentation

Documentation pointing to the registerNetwork() overload including a
timeout argument was pointing to the version removed by commit
15fd4395. This makes it impossible to
cherry pick 15fd4395 due to the linter
complaining about unresolvable links.

This patch fixes the documentation to point to the registerNetwork()
with argument types NetworkRequest, NetworkCallback, int, in that order.

Bug: 36370941
Test: no functional change
Change-Id: Ieaf58f81d89fdf63f480fd15e65ed52822fc4f51