Fall back from mknod() to socket()/bind() on EPERM for SOCK_STREAM.

Apparently OS X is throwing EPERM for mknod(... SOCK_STREAM), and the
current OS X manpage does state that mknod() requires superuser
privileges.

Thanks to Zoran Zaric <zz@zoranzaric.de> for the report.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>