[master] removed 'using namespace boost' as it would hide uint16_t on some versions of boost.

the rest of code actually didn't need this directive, so the removal shouldn't
do any harm anyway.

src/lib/asiodns/sync_udp_server.cc

@@ -32,7 +32,6 @@
 #include <errno.h>
 
 using namespace std;
-using namespace boost;
 using namespace isc::asiolink;
 
 namespace isc {