vendor: Update golang.org/x/net/ipv6

vendor/golang.org/x/net/ipv6/bpf_test.go

vendor/golang.org/x/net/ipv6/bpfopt_linux.go

vendor/golang.org/x/net/ipv6/control.go

vendor/golang.org/x/net/ipv6/control_rfc2292_unix.go

vendor/golang.org/x/net/ipv6/control_rfc3542_unix.go

vendor/golang.org/x/net/ipv6/control_stub.go

vendor/golang.org/x/net/ipv6/control_unix.go

vendor/golang.org/x/net/ipv6/control_windows.go

vendor/golang.org/x/net/ipv6/defs_darwin.go

vendor/golang.org/x/net/ipv6/defs_dragonfly.go

vendor/golang.org/x/net/ipv6/defs_freebsd.go

vendor/golang.org/x/net/ipv6/defs_linux.go

vendor/golang.org/x/net/ipv6/defs_netbsd.go

vendor/golang.org/x/net/ipv6/defs_openbsd.go

vendor/golang.org/x/net/ipv6/defs_solaris.go

vendor/golang.org/x/net/ipv6/dgramopt_posix.go

vendor/golang.org/x/net/ipv6/dgramopt_stub.go

vendor/golang.org/x/net/ipv6/doc.go

vendor/golang.org/x/net/ipv6/endpoint.go

vendor/golang.org/x/net/ipv6/gen.go