accept4-tests: fix to avoid non portable flags * tests/test-accept4.c (main): Pass only SOCK_* flags to accept4(), as they are the only documented ones, and passing others may trigger EINVAL (seen on FreeBSD 10.1-RELEASE). * doc/glibc-functions/accept4.texi: Mention that we don't provide the SOCK_CLOEXEC or SOCK_NONBLOCK defines.