ITS#4357 Solaris occasionally returns ENOSYS when selecting on a descriptor

ITS#4357 Solaris occasionally returns ENOSYS when selecting on a descriptor
in the midst of closing. Instead of special casing EBADF, ENOSYS, and
WSAENOTSOCK, just count if any error occurs two or more times in a row,
and log if so. Don't treat any error as fatal unless it occurs many times
in a row (SLAPD_EBADF_LIMIT).