[netstack_tests] Add component manifests Tests: run-test-component fuchsia-pkg://fuchsia.com/netstack_tests#meta/netstack_loopback_test.cmx run-test-component fuchsia-pkg://fuchsia.com/netstack_tests#meta/netstack_gonet_test.cmx run-test-component fuchsia-pkg://fuchsia.com/netstack_tests#meta/netstack_getaddrinfo_test.cmx run-test-component fuchsia-pkg://fuchsia.com/netstack_tests#meta/netstack_getsockname_test.cmx Change-Id: I8fadae5fe1a7ca4efdebe2d973783e88e1cbb8ea