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
8ff032b990