The sample code on the online documentation fails. Here is a shorter example which fails in the same way:

$s = socket(AF_INET, SOCK_STREAM, 0);
$err = bind($s, "192.168.1.2", 44444);
if ($err)
    die(strerror($err));

reports: Address family not supported by protocol family.

The same thing happens for other values of address and port, or using protocol 6 instead of 0.

I noticed that it is possible to call listen() without successfully calling bind(), in which case the socket listens correctly on a random port number. (is this intentional?)

I also tried using the undocumented function open_listen_sock() instead (with the CGI version of php invoked from the shell), which works once but then fails on future invocations with the same port number, even though the socket and its accepted sockets were closed properly with close().

My configure line:
./configure --with-mcrypt --with-mhash --with-mysql=../../mysql --with-gd --enable-versioning --with-ttf --enable-debug --enable-shared --enable-freetype-4bit-antialias-hack --with-informix --with-bz2 --with-gmp --with-zlib --with-config-file-path=/usr/local/lib/cgiphp.ini --enable-sockets