Win32: Visual Studio 2013 build fix

Apparently Visual Studio 2013 does not support goto <typedef name>.
Hence rename the UINT label. For consistency reasons, also rename
the OCT label.
MinGW: Build fix

Apparently with recent MinGW header files <winsock2.h> should be
included instead of <winsock.h>. Modify <net-snmp/types.h> accordingly.