Ensure EBADF returns for socket functions on mingw.

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.