Add netd-client for tethering apex and update allowed-deps.txt

Split some code from Tethering apex to frameworks/libs/net and
have a new library(netd-client) for it. So basically, netd-client
contains code which was already in Tethering apex.
netd-client also links to netd_event_listener_interface-java, so
netd_event_listener_interface-java is also added into
allowed-deps.txt.

Bug: 174837473
Test: Manual test and check the log.
Change-Id: I31a467f02a8f3049e005d771d61f3d990ac9b8ba