net/ToString: move UnmapV4() to class IPv6Address

src/net/SocketAddress.cxx

@@ -33,6 +33,7 @@
 #include "IPv6Address.hxx"
 #include "util/StringView.hxx"
 
+#include <assert.h>
 #include <string.h>
 
 #ifdef HAVE_UN
@@ -104,6 +105,14 @@ SocketAddress::IsV4Mapped() const noexcept
 	return GetFamily() == AF_INET6 && IPv6Address::Cast(*this).IsV4Mapped();
 }
 
+IPv4Address
+SocketAddress::UnmapV4() const noexcept
+{
+	assert(IsV4Mapped());
+
+	return IPv6Address::Cast(*this).UnmapV4();
+}
+
 unsigned
 SocketAddress::GetPort() const noexcept
 {