[CLATJ#6] libclat: move configure_packet_socket() from netd to apex

configure_packet_socket() is moved from ClatdController. Only change
the failure return value from errno to -errno. The remaining parts
are the same.

The test is modified from ClatdControllerTest::ConfigureIpv6Address.
Simply set socket filter to an interface and check that the packet
socket is bound to the interface. We can't check the socket filter
because there is no way to fetch it from the kernel.

Bug: 212345928
Test: build and boot
      atest libclat_test
Change-Id: Ia33c21051b040829c7d2aa55ed5b7de8766c98c5
4 files changed