Ensure EBADF returns for socket functions on mingw. * lib/accept.c (rpl_accept): Fail with error EBADF if the file descriptor is invalid. * lib/bind.c (rpl_bind): Likewise. * lib/connect.c (rpl_connect): Likewise. * lib/getpeername.c (rpl_getpeername): Likewise. * lib/getsockname.c (rpl_getsockname): Likewise. * lib/getsockopt.c (rpl_getsockopt): Likewise. * lib/listen.c (rpl_listen): Likewise. * lib/recv.c (rpl_recv): Likewise. * lib/recvfrom.c (rpl_recvfrom): Likewise. * lib/send.c (rpl_send): Likewise. * lib/sendto.c (rpl_sendto): Likewise. * lib/setsockopt.c (rpl_setsockopt): Likewise. * lib/shutdown.c (rpl_shutdown): Likewise.