socket: use accept4 when available

socket: use accept4 when available

Linux, *BSD, and Solaris support accept4 system call that enables the
caller to assign additional flags and save some extra system calls. It
can come in handy when O_NONBLOCK or/and FD_CLOEXEC is/are required on a
socket after being accepted.

Ref:
https://man7.org/linux/man-pages/man2/accept.2.html
https://man.freebsd.org/cgi/man.cgi?query=accept4
https://man.dragonflybsd.org/?command=accept&section=2
https://man.openbsd.org/accept.2
https://man.netbsd.org/accept.2
https://docs.oracle.com/cd/E88353_01/html/E37843/accept4-3c.html
https://www.gnu.org/software/gnulib/manual/html_node/accept4.html

Closes #16979