QNativeSocketEngine: fix build with FreeBSD: sockaddr_dl wasn't declared

This partially reverts fcb548878b.

qnativesocketengine_unix.cpp:872:40: error: unknown type name
'sockaddr_dl'; did you mean 'sockaddr_in'?

Pick-to: 6.6
Change-Id: Ifeb6206a9fa04424964bfffd178844096ee7741b
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/network/socket/qnativesocketengine_unix.cpp

@@ -31,6 +31,9 @@
 #include <sys/socket.h>
 #include <netinet/sctp.h>
 #endif
+#ifdef Q_OS_BSD4
+#  include <net/if_dl.h>
+#endif
 
 QT_BEGIN_NAMESPACE