socket: win32 keepalive defs for mingw32
socket: win32 keepalive defs for mingw32

markokr/libusual,rabbitt/libusual,ifduyue/libusual,mgjv/libusual,ifduyue/libusual,markokr/libusual,rabbitt/libusual,rabbitt/libusual,mgjv/libusual,ifduyue/libusual,mgjv/libusual,ifduyue/libusual,rabbitt/libusual,markokr/libusual,markokr/libusual,mgjv/libusual